The family of bird lice is a very extensive one, embracing many genera, and several hundred species. One or more species infest the skin of all our domestic and wild mammals and birds, some birds sheltering beneath their feathers four or five species of lice. Before giving a hasty account of some of our more common species; we will give a sketch of the embryological history of the lice, with special reference to the structure of the mouth parts.
The eggs (Fig. 114, egg of the head louse) are long, oval, somewhat pear-shaped, with the hinder end somewhat pointed, while the anterior end is flattened, and bears little conical micropyles (m, minute orifices for the passage of the spermatozoa into the egg), which vary in form in the different species and genera; the opposite end of the egg is provided with a few bristles. The female attaches her eggs to the hairs or feathers of her host.
After the egg has been fertilized by the male, the blastoderm, or primitive skin, forms, and subsequently two layers, or embryonal membranes, appear; the outer is called the amnion (Fig. 114, am), while the inner visceral membrane (db) partially wraps the rude form of the embryo in its folds. The head (vk) of the embryo is now directed towards the end of the egg on which the hairs are situated; afterwards the embryo revolves on its axis and the head lies next to the opposite end of the egg. Eight tubercles bud out from the under side of the head, of which the foremost and longest are the antennae (as), those succeeding are the mandibles, maxillae, and second maxillae, or labium. Behind them arise six long, slender tubercles forming the legs, and the primitive streak rudely marks the lower wall of the thorax and abdomen not yet formed. Figure 115 represents the head and mouth parts of the embryo of the same louse; vk is the forehead, or clypeus; ant, the antennae; mad, the mandibles; max1, the first pair of maxillae, and max^2, the second pair of maxillae, or labium. Figure 116 represents the mouth parts of the same insect a little farther advanced, with the jaws and labium elongated and closely folded together. Figure 117 represents the same still farther advanced; the mandibles (mad) are sharp, and resemble the jaws of the Mallophaga; and the maxillae (max^1) and labium (max^2) are still large, while afterwards the labium becomes nearly obsolete. Figure 118 represents a front view of the mouth parts of a bird louse, Goniodes; lb, is the upper lip, or labrum, lying under the clypeus; mad, the mandibles; max, the maxillae; l, the lyre-formed piece; and pl, the "plate."
We will now describe some of the common species of lice found on a few of our domestic animals, and the mallophagous parasites occurring on certain mammals and birds. The family Pediculina, or true lice, is higher than the bird lice, their mouth parts, as well as the structure of the head, resembling the true Hemiptera, especially the bed bug. The clypeus, or front of the head, is much smaller than in the bird lice, the latter retaining the enlarged forehead of the embryo, it being in some species half as large as the rest of the head.
All of our domestic mammals and birds are plagued by one or more species of lice. Figure 119 represents the Haematopinus vituli, which is brownish in color. As the specimen figured came from the Burnett collection of the Boston Society of Natural History, together with those of the goat louse, the louse of the common fowl, and of the cat, they are undoubtedly naturalized here. Quite a different species is the louse of the hog (H. suis, Fig. 120).
The remaining parasites belong to the skin-biting lice, or Mallophaga, and I will speak of the several genera referred to in their natural order, beginning with the highest form and that which is nearest allied to Pediculus.
The common barn-yard fowl is infested by a louse that we have called Goniocotes Burnettii (Fig. 121), in honor of the late Dr. W. I. Burnett, a young and talented naturalist and physiologist, who paid more attention than any one else in this country to the study of these parasites, and made a large collection of them, now in the museum of the Boston Society of Natural History. It differs from the G. hologaster of Europe, which lives on the same bird, in the short second joint of the antennae, which are also stouter; and in the long head, the clypeus being much longer and more acutely rounded; while the head is less hollowed out at the insertion of the antennae. The abdomen is oval, and one-half as wide as long, with transverse, broad, irregular bands along the edges of the segments. The mandibles are short and straight, two toothed. The body is slightly yellowish, and variously streaked and banded with pitchy black. The duck is infested by a remarkably slender form (Fig. 122, Philopterus squalidus). Figure 123 represents the louse of the cat, and another species (Fig. 124) of the same genus (Trichodes) lives upon the goat.
The most degraded genus is Gyropus. Mr. C. Cook has found Gyropus ovalis of Europe abundant on the Guinea pig. A species is also found on the porpoise; an interesting fact, as this is the only insect we know of that lives parasitically on any marine animal.
The genus Goniodes (Fig. 125, G. stylifer, the turkey louse) is of great interest from a morphological and developmental point of view, as the antennae are described and figured by Denny as being "in the males cheliform (Fig. 126, a, male; b, female); the first joint being very large and thick, the third considerably smaller, recurved towards the first, and forming a claw, the fourth and fifth very small, arising from the back of the third." He farther remarks, that "the males of this [which lives on the turkey] and all the other species of Goniodes, use the first and third joints of the antennae with great facility, acting the part of a finger and thumb." The antennae of the females are of the ordinary form. This hand-like structure, is, so far as we know, without a parallel among insects, the antennae of the Hemiptera being almost uniformly filiform, and from two to nine-jointed. The design of this structure is probably to enable the male to grasp its consort and also perhaps to cling to the feathers, and thus give it a superiority over the weaker sex in its advances towards courtship. Why is this advantage possessed by the males of this genus alone? The world of insects, and of animals generally abounds in such instances, though existing in other organs, and the developmentist dimly perceives in such departures from a normal type of structure, the origin of new generic forms, whether due at first to a seemingly accidental variation, or, as in this instance, perhaps, to long use as prehensile organs through successive generations of lice having the antennae slightly diverging from the typical condition, until the present form has been developed. Another generation of naturalists will perhaps unanimously agree that the Creator has thus worked through secondary laws, which many of the naturalists of the present day are endeavoring, in a truly scientific and honest spirit of inquiry, to discover.
In their claw or leg-like form these male antennae also repeat in the head, the general form of the legs, whose prehensile and grasping functions they assume. We have seen above that the appendages of the head and thorax are alike in the embryo, and the present case is an interesting example of the unity of type of the jointed appendages of insects, and articulates generally.
Another point of interest in these degraded insects is, that the process of degradation begins either late in the life of the embryo or during the changes from the larval to the adult, or winged state. An instance of the latter may be observed in the wingless female of the canker worm, so different from the winged male; this difference is created after the larval stage, for the caterpillars of both sexes are the same, so far as we know. So with numerous other examples among the moths. In the louse, the embryo, late in its life, resembles the embryos of other insects, even Corixa, a member of a not remotely allied family. But just before hatching the insect assumes its degraded louse physiognomy. The developmentist would say that this process of degradation points to causes acting upon the insect just before or immediately after birth, inducing the retrogression and retardation of development, and would consider it as an argument for the evolution of specific forms by causes acting on the animal while battling with its fellows in the struggle for existence, and perhaps consider that the metamorphoses of the animal within the egg are due to a reflex action of the modes of life of the ancestors of the animal on the embryos of its descendants.
Ha! whare ye gaun, ye crowlin ferlie! Your impudence protects you sairly: I canna say but ye struift rarely, Owre gauze and lace; Tho' faith, I fear ye dine but sparely On sic a place.
Ye ugly, creepin, blastic wormer, Detested, shunn'd by saunt and sinner, How dare ye set your fit upon her Sae fine a lady! Gae somewhere else and seek your dinner On some poor body.
(To a Louse.—Burns.)]
[Footnote 6: We notice while preparing this article that a journal of Parasitology has for some time been issued in Germany—that favored land of specialists. It is the "Zeitschrift fur Parasitenkunde," edited by Dr. E. Hallier and F A. Zurn. 8vo, Jena.]
[Footnote 7: Figure 111 represents the parts of the mouth in a large specimen of Pediculus vestimenti, entirely protruding, and seen from above, magnified one hundred and sixty times; aa, the summit of the head with four bristles on each side; bb, the chitinous band, and c, the hind part of the lower lip, such as they appear through the skin by strong transmitted light; dd, the foremost protruding part of the lower lip (the haustellum); ee, the hooks turned outwards; f, the inner tube of suction, slightly bent and twisted; the two pairs of jaws are perceived on the outside as thin lines; a few blood globules are seen in the interior of the tube.]
THE DRAGON FLY.
Were we to select from among the insects a type of all that is savage, relentless, and bloodthirsty, the Dragon fly would be our choice. From the moment of its birth until its death, usually a twelve-month, it riots in bloodshed and carnage. Living beneath the waters perhaps eleven months of its life, in the larva and pupa states, it is literally a walking pitfall for luckless aquatic insects; but when transformed into a fly, ever on the wing in pursuit of its prey, it throws off all concealment, and reveals the more unblushingly its rapacious character.
Not only do its horrid visage and ferocious bearing frighten children, who call it the "Devil's Darning-needle," but it even distresses older persons, so that its name has become a byword. Could we understand the language of insects, what tales of horror would be revealed! What traditions, sagas, fables, and myths must adorn the annals of animal life regarding this Dragon among insects!
To man, however, aside from its bad name and its repulsive aspect, which its gay trappings do not conceal, its whole life is beneficent. It is a scavenger, being like that class ugly and repulsive, and holding literally, among insects, the lowest rank in society. In the water, it preys upon young mosquitoes and the larvae of other noxious insects. It thus aids in maintaining the balance of life, and cleanses the swamps of miasmata, thus purifying the air we breathe. During its existence of three or four weeks above the waters, its whole life is a continued good to man. It hawks over pools and fields and through gardens, decimating swarms of mosquitoes, flies, gnats, and other baneful insects. It is a true Malthus' delight, and, following that sanguinary philosopher, we may believe that our Dragon fly is an entomological Tamerlane or Napoleon sent into the world by a kind Providence to prevent too close a jostling among the myriads of insect life.
We will, then, conquer our repugnance to its ugly looks and savage mien, and contemplate the hideous monstrosity,—as it is useless to deny that it combines the graces of the Hunchback of Notre Dame and Dickens' Quilp, with certain features of its own,—for the good it does in Nature.
Even among insects, a class replete with forms the very incarnation of ugliness and the perfection of all that is hideous in nature, our Dragon fly is most conspicuous. Look at its enormous head, with its beetling brows, retreating face, and heavy under jaws,—all eyes and teeth,—and hung so loosely on its short, weak neck, sunk beneath its enormous hunchback,—for it is wofully round-shouldered,—while its long, thin legs, shrunken as if from disease, are drawn up beneath its breast, and what a hobgoblin it is!
Its gleaming wings are, however, beautiful objects. They form a broad expanse of delicate parchment-like membrane drawn over an intricate network of veins. Though the body is bulky, it is yet light, and easily sustained by the wings. The long tail undoubtedly acts as a rudder to steady its flight.
These insects are almost universally dressed in the gayest colors. The body is variously banded with rich shades of blue, green, and yellow, and the wings give off the most beautiful iridescent and metallic reflections.
During July and August the various species of Libellula and its allies most abound. The eggs are attached loosely in bunches to the stems of rushes and other water-plants. In laying them, the Dragon fly, according to Mr. P. R. Uhler's observations, "alights upon water-plants, and, pushing the end of her body below the surface of the water, glues a bunch of eggs to the submerged stem or leaf. Libellula auripennis I have often seen laying eggs, and I think I was not deceived in my observation that she dropped a bunch of eggs into the open ditch while balancing herself just a little way above the surface of the water. I have, also, seen her settled upon the reeds in brackish water with her abdomen submerged in part, and there attaching a cluster of eggs. I feel pretty sure that L. auripennis does not always deposit the whole of her eggs at one time, as I have seen her attach a cluster of not more than a dozen small yellow eggs. There must be more than one hundred eggs in one of the large bunches. The eggs of some of the Agrions are bright apple-green, but I cannot be sure that I have ever seen them in the very act of oviposition. They have curious habits of settling upon leaves and grass growing in the water, and often allow their abdomens to fall below the surface of the water; sometimes they fly against the surface, but I never saw what I could assert to be the projecting of the eggs from the body upon plants or into the water. The English entomologists assert that the female Agrion goes below the surface to a depth of several inches to deposit eggs upon the submerged stems of plants." The Agrions, however, according to Lucaze Duthiers, a French anatomist, make, with the ovipositor, a little notch in the plant upon which they lay their eggs.
These eggs soon hatch, probably during the heat of summer. The larva is very active in its habits, being provided with six legs, attached to the thorax, on the back of which are the little wing-pads, or rudimentary wings. The large head is provided with enormous eyes, while a pair of simple, minute eyelets (ocelli) are placed near the origin of the small bristle-like feelers, or antennae. Seen from beneath, instead of the formidable array of jaws and accessory organs commonly observed in most carnivorous larvae, we see nothing but a broad, smooth mask covering the lower part of the face; as if from sheer modesty our young Dragon fly was endeavoring to conceal a gape. But wait a moment. Some unwary insect comes within striking distance. The battery of jaws is unmasked, and opens upon the victim. This mask (Fig. 127) is peculiar to the young, or larva and pupa of the Dragon fly. It is the labium, or under lip greatly enlarged, and armed at the broad spoon-shaped extremity (Fig. 127, x) with two sharp hooks, adapted for seizing and retaining its prey. At rest, the terminal half is so bent up as to conceal the face, and thus the creature crawls about, to all appearance, the most innocent and lamb-like of insects.
Not only does the immature Dragon fly walk over the bottom of the pool or stream it inhabits, but it can also leap for a considerable distance, and by a most curious contrivance. By a syringe-like apparatus lodged in the end of the body, it discharges a stream of water for a distance of two or three inches behind it, thus propelling the insect forwards. This apparatus combines the functions of locomotion and respiration. There are, as usual, two breathing pores (stigmata) on each side of the thorax. But the process of breathing seems to be mostly carried on in the tail. The tracheae are here collected in a large mass, sending their branches into folds of membrane lining the end of the alimentary canal, and which act like a piston to force out the water. The entrance to the canal is protected by three to five triangular horny valves (Fig. 128, 9, 10, 128 a, side view), which open and shut at will. When open, the water flows in, bathing the internal gill-like organs, which extract the air from the water, which is then suddenly expelled by a strong muscular effort.
In the smaller forms, such as Agrion (A. saucium, Fig. 129; Fig. 129 b, side view of false gill, showing but one leaf), the respiratory leaves, called the tracheary, or false-gills, are not enclosed within the body, but form three broad leaves, permeated by tracheae, or air-vessels. They are not true gills, however, as the blood is not aerated in them. They only absorb air to supply the tracheae, which aerate the blood only within the general cavity of the body. These false gills also act as a rudder to aid the insect in swimming.
It is interesting to watch the Dragon flies through their transformations, as they can easily be kept in aquaria. Little, almost nothing, is known regarding their habits, and any one who can spend the necessary time and patience in rearing them, so as to trace up the different stages from the larva to the adult fly, and describe and figure them accurately, will do good service to science.
Mr. Uhler states that at present we know but little of the young stages of our species, but the larva and pupa of the Libellulas may be always known from the AEschnas by the shorter, deeper and more robust form, and generally by their thick clothing of hair. Figure 130 represents the pupa of Cordulia lateralis, and figure 131 that of a Dragon fly referred doubtfully to the genus Didymops. For descriptions and figures of other forms the reader may turn to Mr. Louis Cabot's essay "On the Immature State of the Odonata," published by the Museum of Comparative Zoology at Cambridge.
The pupa scarcely differs from the larva, except in having larger wing-pads (Fig. 132). It is still active, and as much of a gourmand as ever. When the insect is about to assume the pupa state, it moults its skin. The body having outgrown the larva skin, by a strong muscular effort a rent opens along the back of the thorax, and the insect having fastened its claws into some object at the bottom of the pool, the pupa gradually works its way out of the larva-skin. It is now considerably larger than before. Immediately after this tedious operation, its body is soft, but the crust soon hardens. This change, with most species, probably occurs early in summer.
When about to change into the adult fly, the pupa climbs up some plant near the surface of the water. Again its back yawns wide open, and from the rent our Dragon fly slowly emerges. For an hour or more, it remains torpid and listless, with its flabby, soft wings remaining motionless. The fluids leave the surface, the crust hardens and dries, rich and varied tints appear, and our Dragon fly rises into its new world of light and sunshine a gorgeous, but repulsive being. Tennyson thus describes these changes in "The Two Voices":—
To-day I saw the Dragon fly Come from the wells where he did lie. An inner impulse rent the veil Of his old husk: from head to tail Came out clear plates of sapphire mail.
He dried his wings; like gauze they grew; Through crofts and pastures wet with dew A living flash of light he flew.
Of our more common, typical forms of Dragon flies, we figure a few, commonly observed during the summer. The three-spotted Dragon fly (Libellula trimaculata), of which figure 133 represents the male, is so called from the three dark clouds on the wings of the female. But the opposite sex differs in having a dark patch at the front edge of the wings, and a single broad cloud just beyond the middle of the wing.
Libellula quadrimaculata, the four-spotted Dragon fly (Fig. 134), is seen on the wing in June, flying through dry pine woods far from any standing water.
The largest of our Dragon flies are the "Devil's Darning-needles," Eschna heros and grandis, seen hawking about our gardens till dusk. They frequently enter houses, carrying dismay and terror among the children. The hind-body is long and cylindrical, and gaily colored with bright green and bluish bands and spots.
One of our most common Dragon flies is the ruby Dragon fly, Diplax rubicundula, which is yellowish-red. It is seen everywhere flying over pools, and also frequents dry sunny woods and glades. Another common form is Diplax Berenice (Fig. 135 male, Fig. 136 female. The accompanying cut (137) represents the larva, probably of this species, according to Mr. Uhler.) It is black, the head blue in front, spotted with yellow, while the thorax and abdomen are striped with yellow. There are fewer stripes on the body of the male, which has only four large yellow spots on each side of the abdomen. Still another pretty species is Diplax Elisa (Fig. 138). It is black, with the head yellowish and with greenish-yellow spots on the sides of the thorax and base of the abdomen. There are three dusky spots on the front edge of each wing, and a large cloud at the base of the hind pair towards the hind angles of the wing.
Rather a rare form, and of much smaller stature is the Nannophya bella (Fig. 138, female). It was first detected in Baltimore, and we afterwards found it not unfrequently by a pond in Maine. Its abdomen is unusually short, and the reticulations of the wings are large and simple. The female is black, while the male is frosted over with a whitish powder. Many more species of this family are found in this country, and for descriptions of them we would refer the reader to Dr. Hagen's "Synopsis of the Neuroptera of North America," published by the Smithsonian Institution.
The Libellulidae, or family of Dragon flies, and the Ephemeridae, or May flies (Fig. 140), are the most characteristic of the Neuroptera, or veiny-winged insects. This group is a most interesting one to the systematist, as it is composed of so many heterogeneous forms which it is almost impossible to classify in our rigid and at present necessarily artificial systems. We divide them into families and sub-families, genera and sub-genera, species and varieties, but there is an endless shifting of characters in these groups. The different groups would seem well limited after studying certain forms, when to the systematist's sorrow, here comes a creature, perhaps mimicking an ant, or aphis, or other sort of bug, or even a butterfly, and for which they would be readily mistaken by the uninitiated. Bibliographers have gone mad over books that could not be classified. Imagine the despair of an insect-hunter and entomophile, as he sits down to his box of dried neuroptera. He seeks for a true neuropter in the white ant before him, but its very form and habits summon up a swarm of true ants; and then the little wingless book louse (Atropos, Fig. 141) scampering irreverently over the musty pages of his Systema Naturae, reminds him of that closest friend of man—Pediculus vestimenti. Again, his studies lead him to that gorgeous inhabitant of the South, the butterfly-like Ascalaphus, with its resplendent wings, and slender, knobbed antennae so much like those of butterflies, and visions of these beautiful insects fill his mind's eye; or sundry dun-colored caddis flies, modest, delicate neuroptera, with finely fringed wings and slender feelers, create doubts as to whether they are not really allies of the clothes moth, so close is the resemblance.
Thus the student is constantly led astray by the wanton freaks Nature plays, and becomes sceptical as regards the truth of a natural system, though there is one to be discovered; and at last disgusted with the stiff and arbitrary systems of our books,—a disgust we confess most wholesome, if it only leads him into a closer communion with nature. The sooner one leaves those maternal apron-strings,—books,—and learns to identify himself with nature, and thus goes out of himself to affiliate with the spirit of the scene or object before him,—or, in other words, cultivates habits of the closest observation and most patient reflection,—be he painter or poet, philosopher or insect-hunter of low degree, he will gain an intellectual strength and power of interpreting nature, that is the gift of true genius.
MITES AND TICKS.
But few naturalists have busied themselves with the study of mites. The honored names of Hermann, Von Heyden, Duges, Dujardin and Pagenstecher, Nicolet, Koch and Robin, and the lamented Claparede of Geneva, lead the small number who have published papers in scientific journals. After these, and except an occasional note by an amateur microscopist who occasionally pauses from his "diatomaniacal" studies, and looks upon a mite simply as a "microscopic object," to be classed in his micrographic Vade Mecum with mounted specimens of sheep's wool, and the hairs of other quadrupeds, a distorted proboscis of a fly, and podura scales, we read but little of mites and their habits. But few readers of our natural history text-books learn from their pages any definite facts regarding the affinities of these humble creatures, their organization and the singular metamorphosis a few have been known to pass through. We shall only attempt in the present article to indicate a few of the typical forms of mites, and sketch, with too slight a knowledge to speak with much authority, an imperfect picture of their appearance and modes of living.
Mites are lowly organized Arachnids. This order of insects is divided into the Spiders, the Scorpions, the Harvestmen and the Mites (Acarina). They have a rounded oval body, without the usual division between the head-thorax and abdomen observable in spiders, the head-thorax and abdomen being merged in a single mass. There are four pairs of legs, and the mouth parts consist, as seen in the adjoining figure of a young tick (Fig. 142, young Ixodes albipictus), of a pair of maxillae (c), which in the adult terminates in a two or three-jointed palpus, or feeler; a pair of mandibles (b), often covered with several rows of fine teeth, and ending in three or four larger hooks and a serrated labium (a). These parts form a beak which the mite or tick insinuates into the flesh of its host, upon the blood of which it subsists. While many of the mites are parasitic on animals, some are known to devour the eggs of insects and other mites, thrusting their beaks into the egg, and sucking the contents. We have seen a mite (Nothrus ovivorus, Fig. 143) busily engaged in destroying the eggs of a moth like that of the Canker worm, and Dr. Shimer has observed the Acarus? malus sucking the eggs of the Chinch bug. I have also observed another mite devouring the Aphides on the rose leaves in my garden, so that a few mites may be set down as beneficial to vegetation. While a few species are injurious to man, the larger part are beneficial, being either parasitic and baneful to other noxious animals, or more directly useful as scavengers, removing decaying animal and vegetable substances.
The transformations of the mites are interesting to the philosophic zoologist, since the young of certain forms are remarkably different from the adults, and in reaching the perfect state the mite passes through a metamorphosis more striking than that of many insects. The young on leaving the egg have six legs, as we have seen in the case of the Ixodes. Sometimes, however, as, for example, in the larva, as we may call it, of a European mite, Typhlodromus pyri, the adult of which, according to A. Scheuten, is allied to Acarus, and lives under the epidermis of the leaves of the pear in Europe (while Mr. T. Taylor, of the Department of Agriculture at Washington, has found a species in the pear leaves about Washington, and still another form in peach leaves), there are but two pairs of legs present, and the body is long, cylindrical and in a degree worm-like.
I have had the good fortune to observe the different stages of a bird mite, intermediate in its form between the Acarus and Sarcoptes, or Itch mite. On March 6th, Mr. C. Cooke called my attention to certain little mites which were situated on the narrow groove between the main stem of the barb and the outer edge of the barbules of the feathers of the Downy Woodpecker, and subsequently we found the other forms in the down under the feathers. These long worm-like mites were evidently the young of a singular Sarcoptes-like mite, as they were found on the same specimen of Woodpecker at about the same date, and it is known that the growth of mites is rapid, the metamorphoses, judging by the information which we now possess, occupying usually but a few days.
The young (though there is, probably, a still earlier hexapodous stage) of this Sarcoptid has an elongated, oblong, flattened body, with four short legs, provided with a few bristle-like hairs, and ending in a stalked sucker, by aid of which the mite is enabled to walk over smooth, hard surfaces. The body is square at the end, with a slight median indentation, and four long bristles of equal length. They remained motionless in the groove on the barb of the feather, and when removed seemed very inert and sluggish. A succeeding stage of this mite, which may be called the pupal, is considerably smaller than the larva and looks somewhat like the adult, the body having become shorter and broader. The adult is a most singular form, its body being rudely ovate, with the head sunken between the fore legs, which are considerably smaller than the second pair, while the third pair are twice as large as the second pair, and directed backwards, and the fourth pair are very small, not reaching the extremity of the body, which is deeply cleft and supports four long bristles on each side of the cleft, while other bristles are attached to the legs and body, giving the creature, originally ill-shapen, a haggard, unkempt appearance. The two stigmata or breathing pores open near the cleft in the end of the body, and the external opening of the oviduct is situated between the largest and third pair of legs. No males were observed. In a species of Acarus (Tyroglyphus), somewhat like the Cheese mite, which we have alive at the time of writing, in a box containing the remains of a Lucanus larva, which they seem to have consumed, as both young and old are swarming there by myriads, the young are oval and like the adults, except that they are six-legged, the fourth pair growing out after a succeeding moult.
Such is a brief summary of what has been generally known regarding the metamorphoses of a few species of mites. In a few kinds no males have been found; the females have been isolated after being hatched, and yet have been known to lay eggs, which produced young without the interposition of the males. This parthenogenesis has been noticed in several species.
These insects often suddenly appear in vast numbers on various articles of food and about houses, so as to be very annoying. Mr. J. J. H. Gregory, of Marblehead, Mass., has found a mite allied to the European species here figured (Fig. 144) very injurious to the seeds of the cabbage, which it sucked dry. This is an interesting form, and we have called it Cheyletus seminivorus It is of medium size, and especially noticeable from the tripartite palpi, which are divided into an outer, long, curved, claw-like lobe, with two rounded teeth at the base, and two inner, slender lobes pectinated on the inner side, the third innermost lobe being minute. The beak terminates in a sharp blade-like point.
We have received a Cheyletus-like mite, said to have been "extracted from the human face" in New Orleans. The body is oblong, square behind; the head is long and pointed, while the maxillae end in a long, curved, toothed, sickle-like blade. That this creature has the habits of the itch mite is suggested by the curious, large, hair-like spines with which the body and legs are sparsely armed, some being nearly half as long as the body. These hairs are covered with very fine spinules. Those on the end of the body are regularly spoon-shaped. These strange hairs, which are thickest on the legs, probably assisted the mite in anchoring itself in the skin of its host. We have read no account of this strange and interesting form. It is allied to the Acaropsis Mericourti which lives in the human face.
A species, "apparently of the genus Gamasus," according to Dr. Leidy, has been found living in the ear (at the bottom of the external auditory meatus, and attached to the membrana tympani) of steers. "Whether this mite is a true parasite of the ear of the living ox, or whether it obtained access to the position in which it was found after the death of the ox in the slaughter house, has not yet been determined."
We will now give a hasty glance at the different groups of mites, pausing to note those most interesting from their habits or relation to man.
The most highly organized mite (and by its structure most closely allied to the spider) is the little red garden mite, belonging to the genus Trombidium, to which the genus Tetranychus is also nearly related. Our own species of the former genus have not been "worked up," or in other words identified and described, so that whether the European T. holosericeum Linn. is our species or not, we cannot tell. The larvae of this and similar species are known to live parasitically upon Harvestmen (Phalangium), often called Daddy-long-legs; and upon Aphides, grasshoppers and other insects. Mr. Riley has made known to us through the "American Naturalist" (and from his account our information is taken), the habits of certain young of the garden mite (Trombidium) which are excessively annoying in the Southwestern States. The first is the Leptus? Americanus (Fig. 145), or American Harvest mite. It is only known as yet in the larval or Leptus state, when it is of the form indicated in the cut, and brick red in color. "This species is barely visible with the naked eye, moves readily and is found more frequently upon children than upon adults. It lives mostly on the scalp and under the arm pits, but is frequently found on the other parts of the body. It does not bury itself in the flesh, but simply insinuates the anterior part of the body just under the skin, thereby causing intense irritation, followed by a little red pimple. As with our common ticks, the irritation lasts only while the animal is securing itself, and its presence would afterwards scarcely be noticed but for the pimple which results."
The second species (Fig. 145 b, Leptus? irritans) is also only known in the Leptus stage. It is evidently the larva of a distinct genus from the other form, having enormous maxillae and a broad body; it is also brick red. Mr. Riley says that "this is the most troublesome and, perhaps, best known of the two, causing intense irritation and swelling on all parts of the body, but more especially on the legs and around the ankles. Woe betide the person who, after bathing in the Mississippi anywhere in this latitude, is lured to some green dressing-spot of weeds or grass! He may, for the time, consider himself fortunate in getting rid of mud and dirt, but he will afterwards find to his sorrow that he exchanged them for something far more tenacious in these microscopic Harvest-mites. If he has obtained a good supply of them, he will in a few hours begin to suffer from severe itching, and for the next two or three days will be likely to scratch until his limbs are sore.
"With the strong mandibles and the elbowed maxillae which act like arms, this mite is able to bury itself completely in the flesh, thereby causing a red swelling with a pale pustulous centre containing watery matter. If, in scratching, he is fortunate enough to remove the mite before it enters, the part soon heals. But otherwise the irritation lasts for two, three or four days, the pustulous centre reappearing as often as it is broken.
"The animal itself, on account of its minute size, is seldom seen, and the uninitiated, when first troubled with it, are often alarmed at the symptoms and at a loss to account for them. Fortunately these little plagues never attach themselves to persons in such immense numbers as do sometimes young or so-called 'seed' ticks; but I have known cases where, from the irritation and consequent scratching, the flesh had the appearance of being covered with ulcers; and in some localities, where these pests most abound, sulphur is often sprinkled during 'jigger' season in the boots or shoes as a protection.
"Sulphur ointment is the best remedy against the effects of either of these mites, though when that cannot be obtained, saleratus water and salt water will partially allay the irritation.
"The normal food of either must, apparently, consist of the juices of plants, and the love of blood proves ruinous to those individuals who get a chance to indulge it. For unlike the true Jigger, the female of which deposits eggs in the wound she makes, these Harvest-mites have no object of the kind, and when not killed by the hands of those they torment, they soon die victims to their sanguinary appetite."
Another Leptus-like form is the parasite of the fly, described by Mr. Riley under the name of Astoma? muscarum (Fig. 146). How nearly allied it is to the European Astoma parasiticum we have not the means of judging.
The European Tetranychus telarius Linn., or web-making mite, spins large webs on the leaves of the linden tree. Then succeed in the natural order the water mites (Hydrachna), which may be seen running over submerged sticks and on plants, mostly in fresh water, and rarely on the borders of the sea. The young after leaving the egg differ remarkably from the adults, so as to have been referred to a distinct genus (Achlysia) by the great French naturalist, Audouin. They live as parasites on various water insects, such as Dytiscus, Nepa and Hydrometra, and when mature live free in the water, though Von Baer observed an adult Hydrachna concharum living parasitically on the gills of the fresh-water mussel, Anodon. The species are of minute size. Collectors of beetles often meet with a species of Uropoda attached firmly to their specimens of dung-inhabiting or carrion beetles. It is a smoothly polished, round, flattened mite, with short, thick legs, scarcely reaching beyond the body.
We now come to the Ticks, which comprise the largest mites. The genus Argas closely resembles Ixodes. Gerstaecker states that the Argas Persicus is very annoying to travellers in Persia. The habits of the wood ticks (Ixodes) are well known. Travellers in the tropics speak of the intolerable torment occasioned by these pests which, occurring ordinarily on shrubs and trees, attach themselves to all sorts of reptiles, beasts and cattle, and even man himself as he passes by within their reach. Sometimes cases fall within the practice of the physician, who is called to remove the tick, which is found sometimes literally buried beneath the skin. Mr. J. Stauffer writes me, that "on June 23d the daughter of Abraham Jackson (colored), playing among the leaves in a wood, near Springville, Lancaster County, Penn., on her return home complained of pain in the arm. No attention was paid to it till the next day, when a raised tumor was noticed, a small portion protruding through the skin, apparently like a splinter of wood. The child was taken to Dr. Morency, who applied the forceps, and after considerable pain to the child, and labor to himself, extracted a species of Ixodes, nearly one-quarter of an inch long, and of an oval form and brown mahogany color, with a metallic spot, like silver bronze, centrally on the dorsal region." This tick proved, from Mr. Stauffer's figures, to be, without doubt, Ixodes unipunctata. It has also been found in Massachusetts by Mr. F. G. Sanborn.
Another species is the Ixodes bovis (Fig. 147), the common cattle tick of the Western States and Central America. It is very annoying to horned cattle, gorging itself with their blood, but is by no means confined to them alone, as it lives indifferently upon the rattlesnake, the iguana, small mammals and undoubtedly any other animal that brushes by its lurking-place in the forest. It is a reddish, coriaceous, flattened, seed-like creature, with the body oblong oval, and contracted just behind the middle. When fully grown it measures from a quarter to half an inch in length. We have received it from Missouri, at the hands of Mr. Riley, and Mr. J. A. McNiel has found it very abundantly on horned cattle on the western coast of Nicaragua.
We now come to the genus Acarus (Tyroglyphus), of which the cheese and sugar mites are examples. Some species of Acarian mites have been found in the lungs and blood-vessels, and even the intestinal canal of certain vertebrates, while the too familiar itch insect lurks under the skin of the hand and other parts of the body of certain uncleanly human bipeds.
Many people have been startled by statements in newspapers and more authoritative sources, as to the immense numbers of mites (Acarus sacchari, Fig. 148) found in unrefined or raw sugar. According to Prof. Cameron, of Dublin, as quoted in the "Journal of the Franklin Institute," for November, 1868, "Dr. Hassel (who was the first to notice their general occurrence in the raw sugar sold at London) found them in a living state in no fewer than sixty-nine out of seventy-two samples. He did not detect them in a single specimen of refined sugar. In an inferior sample of raw sugar, examined in Dublin by Mr. Cameron, he reports finding five hundred mites in ten grains of sugar, so that in a pound's weight occurred one hundred thousand of these little creatures, which seem to have devoted themselves with a martyr-like zeal to the adulteration of sugar. They appear as white specks in the sugar. The disease known as grocer's itch is, undoubtedly, due to the presence of this mite, which, like its ally the Sarcoptes, works its way under the skin of the hand, in this case, however, of cleanly persons. Mr. Cameron states that "the kind of sugar which is both healthful and economical, is the dry, large-grained and light-colored variety."
Closely allied to the preceding, is the Cheese mite (Acarus siro Linn.), which often abounds in newly made cheese. Lyonet states that during summer this mite is viviparous. Acarus farinae DeGeer, as its name indicates, is found in flour. Other species have been known to occur in ulcers.
We should also mention the Mange insect of the horse (Psoroptes equi, Fig. 149, much enlarged; a, head more magnified). According to Prof. Verrill it is readily visible to the naked eye and swarms on horses afflicted with the mange, which is a disease analogous to the itch in man. It has a soft, depressed body, spiny beneath at the base of the legs and on the thorax. One or both of the two posterior pairs of feet bear suckers, and all are more or less covered with long, slender hairs. This insect may be destroyed by the same remedies as are used for lice and for the human itch. The best remedy is probably a solution of sulphuret of potassium.
The itch insect (Sarcoptes scabiei, Fig. 150) was first recognized by an Arabian author of the twelfth century, as the cause of the disease which results from its attacks. The body of the insect is rounded, with the two hind pair of feet rudimentary and bearing long hairs. It buries itself in the skin on the more protected parts of the body, and by its punctures maintains a constant irritation. Other species are known to infest the sheep and dog. Another singular mite is the Demodex folliculorum (Fig. 151), which was discovered by Dr. Simon, of Berlin, buried in the diseased follicles of the wings of the nose in man. It is a long, slender, worm-like form, with eight short legs, and in the larva state has six legs. This singular form is one of the lowest and most degraded of the order of Arachnids. A most singular mite was discovered by Newport on the body of a larva of a wild bee, and described by him under the name of Heteropus ventricosus. The body of the fully formed female is long and slender. After attaining this form, its small abdomen begins to enlarge until it assumes a globular form, and the mass of mites look like little beads. Mr. Newport was unable to discover the male, and thought that this mite was parthenogenous. It will be seen that the adult Demodex retains the elongated, worm-like appearance of the larva of the higher mites, such as Typhlodromus. This is an indication of its low rank, and hints of a relationship to the Tardigrades and the Pentastoma, the latter being a degraded mite, and the lowest of its order, living parasitically within the bodies of other animals.
[Footnote 8: The figure at the bottom on the left represents the adult, fully-gorged tick.]
BRISTLE-TAILS AND SPRING-TAILS.
The Thysanura, as the Poduras and their allies, the Lepismas, are called, have been generally neglected by entomologists, and but few naturalists have paid special attention to them. Of all those microscopists who have examined Podura scales as test objects, we wonder how many really know what a Podura is?
In preparing the following account I have been under constant indebtedness to the admirable and exhaustive papers of Sir John Lubbock, in the London "Linnaean Transactions" (vols. 23, 26 and 27). Entomologists will be glad to learn that he is shortly going to press with a volume on the Poduras, which, in distinction from the Lepismas, to which he restricts the term Thysanura, he calls Collembola, in allusion to the sucker-like tubercle situated on the under side of the body, which no other insects are known to possess.
The group of Bristle-tails, as we would dub the Lepismas in distinction from the Spring-tails, we will first consider. They are abundant in the Middle States under stones and leaves in forests, and northward are common in damp houses, while one beautiful species that we have never noticed elsewhere, is our "cricket on the hearth," abounding in the chinks and crannies of the range of our house, and also in closets, where it feeds on sugar, etc., and comes out like cockroaches, at night, shunning the light. Like the cockroaches, which it vaguely resembles in form, this species loves hot and dry localities, in distinction from the others which seek moisture as well as darkness. By some they are called "silver witches," and as they dart off, when disturbed, like a streak of light, their bodies being coated in a suit of shining mail, which the arrangement of the scales resembles, they have really a weird and ghostly look.
The most complicated genus, and the one which stands at the head of the family, is Machilis, one species of which lives in the Northern and Middle States, and another in Oregon. They affect damp places, living under leaves and stones. They all have rounded, highly arched bodies, and large compound eyes, the two being united together. The maxillary palpi are greatly developed, but the chief characteristics are the two-jointed stylets arranged in nine pairs along each side of the abdomen, reminding us of the abdominal legs of Myriopods. The body ends in three long bristles, as in Lepisma.
The Lepisma saccharina of Linnaeus, if, as is probable, that is the name of our common species, is not uncommon in old damp houses, where it has the habits of the cockroach, eating cloths, tapestry, silken trimmings of furniture, and doing occasional damage to libraries by devouring the paste, and eating holes in the leaves and covers of books.
In general form Lepisma may be compared to the larva of Perla, a net-veined Neuropterous insect, and also to the narrow-bodied species of cockroaches, minus the wings. The body is long and narrow, covered with rather coarse scales, and ends in three many jointed anal stylets, or bristles, which closely resemble the many jointed antennae, which are remarkably long and slender. The thermophilous species already alluded to may be described as perhaps the type of the genus, the L. saccharina being simpler in its structure. The body is narrow and flattened; the basal joints of the legs being broad, flat and almost triangular, like the same joints in the cockroaches. The legs consist of six joints, the tarsal joints being large and two in number, and bearing a pair of terminal curved claws. The three thoracic segments are of nearly equal size, and the eight abdominal segments are also of similar size. The tracheae are well developed, and may be readily seen in the legs. The end of the rather long and weak abdomen is propped up by two or three pairs of bristles, which are simple, not jointed, but moving freely at their insertion; thus they take the place of legs, and remind one of the abdominal legs of the Myriopods; and we shall see in certain other genera (Machilis and Campodea) of the Bristle-tails that there are actually two-jointed bristles arranged in pairs along the abdomen. They may probably be directly compared with the abdominal legs of Myriopods. Further study, however, of the homologies of these peculiar appendages, and especially a knowledge of the embryological development of Lepisma and Machilis, is needed before this interesting point can be definitely settled. The three many jointed anal stylets may, however, be directly compared with the similar appendages of Perla and Ephemera. The mode of insertion of the antennae of this family is much like that of the Myriopods, the front of the head being flattened, and concealing the base of the antennae, as in the Centipedes and Pauropus. Indeed, the head of any Thysanurous insect seen from above, bears a general resemblance in some of its features to that of the Centipede and its allies. So in a less degree does the head of the larvae of certain Neuroptera and Coleoptera. The eyes are compound, the single facets forming a sort of heap. The clypeus and labrum, or upper lip, is, in all the Thysanura, carried far down on the under side of the head, the clypeus being almost obsolete in the Poduridae, this being one of the most essential characters of that family. Indeed, it is somewhat singular that these and other important characteristics of this group have been almost entirely passed over by authors, who have consequently separated these insects from other groups on what appear to the writer as comparatively slight and inconsiderable characters. The mouth-parts of the Lepismatidae (especially the thermophilous Lepisma, which we now describe) are most readily compared with those of the larva of Perla. The rather large, stout mandibles are concealed at their tips, under the upper lip, which moves freely up and down when the creature opens its mouth. The mandible is about one-third as broad as long, armed with three sharp teeth on the outer edge, and with a broad cutting edge within, and still further inwards a lot of straggling spinules. In all these particulars, the mandible of Lepisma is comparable with that of certain Coleoptera and Neuroptera. So also are the maxillae and labium, though we are not aware that any one has indicated how close the homology is. The accompanying figure (152) of the maxilla of a beetle may serve as an example of the maxilla of the Coleoptera, Orthoptera and Neuroptera. In these insects it consists almost invariably of three lobes, the outer being the palpus, the middle lobe the galea, and the innermost the lacinia; the latter undergoing the greatest modifications, forming a comb composed of spines and hairs varying greatly in relative size and length. How much the palpi vary in these groups of insects is well known. The galea sometimes forms a palpus-like appendage. Now these three lobes may be easily distinguished in the maxilla of Lepisma. The palpus instead of being directed forward, as in the insects mentioned above (in the pupa of Ephemera the maxilla is much like that of Lepisma), is inserted nearer the base than usual and thrown off at right angles to the maxilla, so that it is stretched out like a leg, and in moving about the insect uses its maxillae partly as supports for its head. They are very long and large, and five or six-jointed. The galea, or middle division, forms a simple lobe, while the lacinia has two large chitinous teeth on the inner edge, and internally four or five hairs arising from a thin edge.
The labium is much as in that of Perla, being broad and short, with a distinct median suture, indicating its former separation in embryonic life into a pair of appendages. The labial palpi are three-jointed, the joints being broad, and in life directed backwards instead of forwards as in the higher insects.
There are five American species of the genus Lepisma in the Museum of the Peabody Academy. Besides the common L. saccharina? there are four undescribed species; one found about out-houses and cellars, and the heat-loving form, perhaps an imported, species, found in a kitchen in Salem, and apparently allied to the L. thermophila Lucas, of houses in Brest, France; and lastly two allied forms, one from Key West, and another from Polvon, Western Nicaragua, collected by Mr. McNiel. The last three species are beautifully ornamented with finely spinulated hairs arranged in tufts on the head; while the sides of the body, and edges of the basal joints of the legs are fringed with them.
The interesting genus Nicoletia stands at the bottom of the group. It has the long, linear, scaleless body of Campodea, in the family below, but the head and its appendages are like Lepisma, the maxillary palpi being five-jointed, and the labial palpi four-jointed. The eyes are simple, arranged in a row of seven on each side of the head. The abdomen ends in three long and many jointed stylets, and there are the usual "false branchial feet" along each side of the abdomen. There are two European species which occur in greenhouses. No species have yet been found in America.
The next family of Thysanura is the Campodeae, comprising the two genera Campodea and Japyx. These insects are much smaller than the Lepismidae, and in some respects are intermediate between that family and the Poduridae (including the Smynthuridae).
In this family the body is long and slender, and the segments much alike in size. There is a pair of spiracles on each thoracic ring. The mandibles are long and slender, ending in three or four teeth, and with the other appendages of the mouth are concealed within the head, "only the tips of the palpi (and of the maxillae when these are opened) projecting a very little beyond the rounded entire margin of the epistoma," according to Haliday. The maxillae are comb-shaped, due to the four slender, minutely ciliated spines placed within the outer tooth. The labium in Japyx is four-lobed and bears a small two-jointed palpus. The legs are five-jointed, the tarsi consisting of a single joint, ending in two large claws. The abdomen consists of ten segments, and in Campodea along each side is a series of minute, two-jointed appendages such as have been described in Machilis. These are wanting in Japyx. None of the species in this family have the body covered with scales. They are white, with a yellowish tinge.
The more complicated genus of the two is Japyx (Fig. 153, Japyx solifugus, found under stones in Southern Europe; a, the mouth from beneath, with the maxillae open; b, maxilla; d, mandible; c, outline of front of head seen from beneath, with the labial palpi in position) which, as remarked by the late Mr. Haliday (who has published an elaborate essay on this genus in the Linnaean Transactions, vol. 24, 1864), resembles Forficula in the large forceps attached to its tail. An American species (J. Saussurii) lives in Mexico, and we look for its discovery in Texas.
Campodea (C. staphylinus Westw., Fig. 154, enlarged; a, mandible; b, maxilla), otherwise closely related, has more rudimentary mouth-parts, and the abdomen ends in two many jointed appendages.
Our common American species of Campodea (C. Americana) lives under stones in damp places. It is yellowish, about a sixth of an inch in length, is very agile in its movements, and would easily be mistaken for a very young Lithobius. A larger species and differing in having longer antennae, has been found by Mr. C. Cooke in Mammoth Cave, and has been described in the "American Naturalist" under the name of Campodea Cookei. Haliday has remarked that this family bears much resemblance to the Neuropterous larva of Perla (Fig. 155), as previously remarked by Gervais; and the many points of resemblance of this family and the Lepismidae to the larval forms of some Neuroptera that are active in the pupa state (the Pseudoneuroptera of Erichson and other authors) are very striking. Campodea resembles the earliest larval form of Chloeon, as figured by Sir John Lubbock, even to the single jointed tarsus; and why these two Thysanurous families should be removed from the Neuroptera we are unable, at present, to understand, as to our mind they scarcely diverge from the Neuropterous type more than the Mallophaga, or biting lice, from the type of Hemiptera.
Haliday, remarking on the opinion of Linnaeus and Schrank, who referred Campodea to the old genus Podura, says with much truth, "it may be perhaps no unfair inference to draw, that the insect in question is in some measure intermediate between both," i. e., Podura and Lepisma. This is seen especially in the mouth-parts which are withdrawn into the head, and become very rudimentary, affording a gradual passage into the mouth-parts of the Poduridae, which we now describe.
The next group, the Podurelles of Nicolet, and Collembola of Lubbock, are considered by the latter, who has studied them with far more care than any one else, as "less closely allied" to the Lepismidae "than has hitherto been supposed." He says "the presence of tracheae, the structure of the mouth and the abdominal appendage; all indicate a wide distinction between the Lepismidae and the Poduridae. We must, indeed, in my opinion, separate them entirely from one another; and I would venture to propose for the group comprised in the old genus Podura, the term Collembola, as indicating the existence of a projection, or mammilla, enabling the creature to attach or glue itself to the body on which it stands." Then without expressing his views as to the position and affinities of the Lepismidae, he remarks "as the upshot of all this, then, while the Collembola are clearly more nearly allied to the Insecta than to the Crustacea or Arachnida, we cannot, I think, regard them as Orthoptera or Neuroptera, or even as true insects. That is to say, the Coleoptera, Orthoptera, Neuroptera, Lepidoptera, etc., are in my opinion, more nearly allied to one another than they are to the Poduridae or Smynthuridae. On the other hand, we certainly cannot regard the Collembola as a group equivalent in value to the Insecta. If, then, we attempt to map out the Articulata, we must, I think, regard the Crustacea and Insecta as continents, the Myriopoda and Collembola as islands—of less importance, but still detached. Or, if we represent the divisions of the Articulata like the branching of a tree, we must picture the Collembola as a separate branch, though a small one, and much more closely connected with the Insecta than with the Crustacea or the Arachnida." Lamarck regarded them as more nearly allied to the Crustacea than Insecta. Gervais, also, in the "Histoire Naturelle des Insectes: Apteres," indicates a considerable diversity existing between the Lepismidae and Poduridae, though they are placed next to each other. Somewhat similar views have been expressed by so high an authority as Professor Dana, who, in the "American Journal of Science" (vol. 37, Jan., 1864), proposed a classification of insects based on the principle of cephalization, and divided the Hexapodous insects into three groups: the first (Ptero-prosthenics, or Ctenopters) comprising the Hymenoptera, Diptera, Aphaniptera (fleas), Lepidoptera, Homoptera, Trichoptera and Neuroptera; the second group (Ptero-metasthenics, or Elytropters) comprising the Coleoptera, Hemiptera and Orthoptera; while the Thysanura compose the third group. Lubbock has given us a convenient historical view of the opinions of different authors regarding the classification of these insects, which we find useful. Nicolet, the naturalist who, previous to Lubbock, has given us the most correct and complete account of the Thysanura, regarded them as an order, equivalent to the Coleoptera or Diptera, for example. In this he followed Latreille, who established the order in 1796. The Abbe Bourlet adopted the same view. On the other hand Burmeister placed the Thysanura as a separate tribe between the Mallophaga (Bird Lice) and Orthoptera, and Gerstaecker placed them among the Orthoptera. Fabricius and Blainville put them with the Neuroptera, and the writer, in his "Guide to the Study of Insects," and previously in 1863, ignorant of the views of the two last named authors, considered the Thysanura as degraded Neuroptera, and noticed their resemblance to the larvae of Perla, Ephemera, and other Neuroptera, such as Rhaphidia and Panorpa, regarding them as standing "in the same relation to the rest of the Neuroptera [in the Linnaean sense], as the flea does to the rest of the Diptera, or the lice and Thrips to the higher Hemiptera."
After having studied the Thysanura enough to recognize the great difficulty of deciding as to their affinities and rank, the writer does not feel prepared to go so far as Dana and Lubbock, for reasons that will be suggested in the following brief account of the more general points in their structure, reserving for another occasion a final expression of his views as to their classification.
The Poduridae, so well known by name, as affording the scales used by microscopists as test objects, are common under stones and wet chips, or in damp places, cellars, mushrooms and about manure heaps. They need moisture, and consequently shade. They abound most in spring and autumn, laying their eggs at both seasons, though most commonly in the spring. During a mild December, they may be found in abundance under sticks and stones, even in situations so far north as Salem, Mass.
The body of the Poduras is rather short and thick, most so in Smynthurus (Fig. 156), and becoming long and slender in Tomocerus and Isotoma. The segments are inclined to be of unequal size, the prothoracic ring sometimes becoming almost obsolete, and some of the abdominal rings are much smaller than others; while in Lipura and Anura, the lowest forms of the group, the segments are all much alike in size.
The head is in form much like that of certain larvae of Neuroptera and of Forficula, an Orthopterous insect. The basal half of the head is marked off from the eye-bearing piece (epicranium) by a V-shaped suture (Fig. 157, head of Degeeria; compare also the head of the larva of Forficula, Fig. 158, in which the suture is the same), and the insertion of the antennae is removed far down the front, near the mouth, the clypeus being very short; this piece, so large and prominent in the higher insects, is not distinctly separated by suture from the surrounding parts of the head, thus affording one of the best distinctive characters of the Poduridae. The eyes are situated on top of the head just behind the antennae, and are simple, consisting of a group of from five to eight or ten united into a mass in Smynthurus, but separated in the Poduridae (see Fig. 176, e, eye of Anurida). The antennae are usually four-jointed, and vary in length in the different genera.
The mouth-parts are very difficult to make out, but by soaking the insect in potash for twenty-four hours, thus rendering the body transparent, they can be satisfactorily observed. They are constructed on the same general type as the mouth-parts of the Neuroptera, Orthoptera and Coleoptera, and except in being degraded, and with certain parts obsolete, they do not essentially differ. On observing the living Podura, the mouth seems a simple ring, with a minute labrum and groups of hairs and spinules, which the observer, partly by guess-work, can identify as jaws and maxillae, and labium. But in studying the parts rendered transparent, we can identify the different appendages. Figure 159 shows the common Tomocerus plumbeus greatly enlarged (Fig. 160, seen from above), and as the mouth-parts of the whole group of Poduras are remarkably constant, a description of one genus will suffice for all. The labrum, or upper lip, is separated by a deep suture from the clypeus, and is trapezoidal in form. The mandibles and maxillae are long and slender, and buried in the head, with the tips capable of being extended out from the ring surrounding the mouth for a very short distance. The mandibles (md, Fig. 159) are like those of the Neuroptera, Orthoptera and Coleoptera in their general form, the tip ending in from three to six teeth (three on one mandible and six on the other), while below, is a rough, denticulated molar surface, where the food seized by the terminal teeth is triturated and prepared to be swallowed. Just behind the mandibles are the maxillae, which are trilobate at the end, as in the three orders of insects above named. The outer lobe, or palpus, is a minute membranous tubercle ending in a hair (Fig. 161, mp), while the middle lobe, or galea, is nearly obsolete, though I think I have seen it in Smynthurus, where it forms a lobe on the outside of the lacinia. The lacinia, or inner lobe (Fig. 161, lc; 162, the same enlarged), in Tomocerus consists of two bundles of spinules, one broad like a ruffle, and the other slender, pencil-like, ending in an inner row of spines, like the spinules on the lacinia of the Japyx and Campodea and, more remotely, the laciniae of the three sub-orders of insects above referred to. There is also a horny, prominent, three-toothed portion (Fig. 161, g). These homologies have never been made before, so far as the writer is aware, but they seem natural, and suggested by a careful examination and comparison with the above-mentioned mandibulate insects.
The spring consists of a pair of three-jointed appendages, with the basal joints soldered together early in embryonic life, while the other two joints are free, forming a fork. It is longest in Smynthurus and Degeeria, and shortest in Achorutes (Fig. 172, b), where it forms a simple, forked tubercle; and is obsolete in Lipura and Anura, its place being indicated by an oval scar. The third joint varies in form, being hairy, serrate and knife-like in form, as in Tomocerus (Fig. 159, a), or minute, with a supplementary tooth, as in Achorutes (Fig. 172, c). This spring is in part homologous with the ovipositor of the higher insects, which originally consists of three pairs of tubercles, each pair arising apparently from the seventh, eighth, and ninth (the latter the penultimate) segments of the abdomen in the Hymenoptera. The spring of the Podura seems to be the homologue of the third pair of these tubercles, and is inserted on the penultimate segment. This comparison I have been able to make from a study of the embryology of Isotoma.
Another organ, and one which, so far as I am aware, has been overlooked by previous observers, I am disposed to consider as possibly an ovipositor. In the genus Achorutes, it may be found in the segment just before the spring-bearing segment, and situated on the median line of the body. It consists (Fig. 163) of two squarish valves, from between which projects a pair of minute tubercles, or blades, with four rounded teeth on the under side. This pair of infinitesimal saws reminds one of the blades of the saw-fly, and I am at a loss what their use can be unless to cut and pierce so as to scoop out a shallow place in which to deposit an egg. It is homologous in situation with the middle pair of blades which composes the ovipositor of higher insects, and if it should prove to be used by the creature in laying its eggs, we should then have, with the spring, an additional point of resemblance to the Neuroptera and higher insects, and instead of this spring being an important differential character, separating the Thysanura from other insects, it binds them still closer, though still differing greatly in representing only a part of the ovipositor of the higher insects. (This is a catch for holding the spring in place.)
But all the Poduras differ from other insects in possessing a remarkable organ situated on the basal segment of the abdomen. It is a small tubercle, with chitinous walls, forming two valves from between which is forced out a fleshy sucker, or, as in Smynthurus, a pair of long tubes, which are capable of being darted out on each side of the body, enabling the insect to attach itself to smooth surfaces, and rest in an inverted position.
The eggs are laid few in number, either singly or several together, on the under side of stones, chips or, as in the case of Isotoma Walkerii, under the bark of trees. They are round, transparent. The development of the embryo of Isotoma in general accords with that of the Phryganeidae and suggests on embryological grounds the near relationship of the Thysanura to the Neuroptera.
The earliest stage observed was at the time of the appearance of the primitive band (Fig. 164, a, b, folding of the primitive band; c, the dotted line crosses the primitive band, and terminates in a large yolk granule) which surrounds the egg as in the Caddis flies. Soon after, the primitive segments appear (Fig. 165; 1, antennae; 2, mandibles; 3, maxillae; the labium was not seen; 5-7, legs; c, yolk surrounded by the primitive band) and seem to originate just as in the Caddis flies. Figure 166 is a front view of the embryo shortly before it is hatched; figure 167, side view of the same, the figures as in Fig. 165; sp, spring; l, labrum. The labrum or upper lip, and the clypeus are large and as distinct as in the embryos of other insects, a fact to which we shall allude again. The large three-jointed spring is now well developed, and the inference is drawn that it represents a pair of true abdominal legs. The embryo when about to hatch throws off the egg-shell and amnion in a few seconds. The larva is perfectly white and is very active in its movements, running over the damp, inner surface of the bark. It is a little over a hundredth of an inch in length, and differs from the adult in being shorter and thicker, with the spring very short and stout. In fact the larva assumes the form of the lower genera of the family, such as Achorutes and Lipura, the adult more closely resembling Degeeria. The larva after its first moult retains its early clumsy form, and is still white. After a second moult it becomes purplish, and much more slender, as in the adult. The eggs are laid and the young hatched apparently within a period of from six to ten days.
Returning to the stage indicated by figures 166 and 167, I am induced to quote some remarks published in the Memoirs of the Peabody Academy of Science, No. 2, p. 18, which seem to support the view that these insects are offshoots from the Neuroptera.
"The front of the head is so entirely different from what it is in the adult, that certain points demand our attention. It is evident that at this period the development of the insect has gone on in all important particulars much as in other insects, especially the Neuropterous Mystacides as described by Zaddach. The head is longer vertically than horizontally, the frontal, or clypeal region is broad, and greater in extent than the epicranio-occipital region. The antennae are inserted high up on the head, next the ocelli, falling down over the clypeal region. The clypeus, however, is merged with the epicranium, and the usual suture between them does not appear distinctly in after life, though its place is seen in figure 167 to be indicated by a slight indentation. The labrum is distinctly defined by a well marked suture, and forms a squarish, knob-like protuberance, and in size is quite large compared to the clypeus. From this time begins the process of degradation, when the insect assumes its Thysanurous characters, which consist in an approach to the form of the Myriopodous head, the front, or clypeal region being reduced to a minimum, and the antennae and eyes brought in closer proximity to the mouth than in any other insects."
Sir John Lubbock has given us an admirable account of the internal anatomy of these little creatures, his elaborate and patient dissections filling a great gap in our knowledge of their internal structure. The space at our disposal only permits us to speak briefly of the respiratory system. Lubbock found a simple system of tracheae in Smynthurus which opens by "two spiracles in the head, opposite the insertion of the antennae," i. e., on the back of the head. (Von Olfers says that they open on the prothorax.) Nicolet and Olfers claim to have found tracheae in several lower genera (Orchesella, Tomocerus, and Achorutes and allied genera), but Lubbock was unable to detect them, and I may add that I have not yet been able after careful search to find them either in living specimens, or those rendered transparent by potash.
Having given a hasty sketch of the external aspect of the Poduras, I extract from Lubbock's work a synopsis of the families and genera for the convenience of the student, adding the names of known American species, or indications of undescribed native forms.
SMYNTHURIDAE.—Body globular or ovoid; thorax and abdomen forming one mass; head vertical or inclined; antennae of four or eight segments. Eyes eight on each side, on the top of the head. Legs long and slender. Saltatory appendage with a supplementary segment.
Smynthurus. Antennae four-jointed, bent at the insertion of the fourth, which is nearly as long as the other three, and appears to consist of many small segments. No conspicuous dorsal tubercles. (In this country Fitch has described five species: S. arvalis, elegans, hortensis, Novaeboracensis, and signifer. Figure 156 represents a species found in Maine.)
Dicyrtoma. Antennae eight-jointed, five before, three after the bend. Two dorsal tubercles on the abdomen.
Papirius. Antennae four-jointed, without a well-marked elbow, and with a short terminal segment offering the appearance of being many-jointed.
PODURIDAE.—This family comprises those species of the old genus Podura, in which the mouth has mandibles [also maxillae and a labium], and the body is elongated, with a more or less developed saltatory appendage at the posterior extremity.
Orchesella. Segments of the body unequal in size, more or less thickly clothed with clubbed hairs. Antennae long, six-jointed. Eyes six in number on each side, arranged in the form of an S. (One or two beautiful species live about Salem.)
Degeeria. Segments of the body unequal in size, more or less thickly clothed by clubbed hairs. Antennae longer than the head and thorax, filiform, four-jointed. Eyes eight in number on each side of the head. (Two species, Degeeria decem-fasciata, Pl. 10, Figs. 2, 3, and D. purpurascens, Figs. 4, 5, are figured in the "Guide to the Study of Insects." Figure 168 represents a species found in Salem, Mass., closely allied to the European D. nivalis. Five species are already known in New England.)
Seira. Body covered with scales. Antennae four-jointed; terminal segment not ringed. Eyes on a dark patch. Thorax not projecting over the head. Abdominal segments unequal.
Templetonia. Segments of the body subequal, clothed by clubbed hairs, and provided with scales. Antennae longer than the head and thorax, five-jointed, with a small basal segment, and with the terminal portion ringed.
Isotoma. Four anterior abdominal segments subequal, two posterior ones small; body clothed with simple hairs and without scales. Antennae four-jointed, longer than the head; segments subequal. Eyes seven in number on each side, arranged in the form of an S. (Three species are found in Massachusetts, one of which (I. plumbea) is figured on Pl. 10, Figs. 6, 7, of the "Guide to the Study of Insects," third edition.)
Tomocerus. Abdominal segments unequal, with simple hairs and scales. Antennae very long, four-jointed, the two terminal segments ringed. Eyes seven in number on each side. (The European T. plumbea, Podura plumbea of authors, is our species, and is common. Fig. 160, greatly enlarged, copied from Templeton; Fig. 159, side view, see also Fig. 161, where the mouth-parts are greatly enlarged, the lettering being the same, md, mandibles; mx, maxillae; mp, maxillary palpus; lb, labium; lp, labial palpus; lc, lacinia; g, portion ending in three teeth; l, lobe of labium; sp, ventral sucking disk; the dotted line's passing through the body represent the course of the intestine; b, end of tibia, showing the tarsus, with the claw, and two accessory spines; a, third joint of the spring. Fig. 162, lacinia of maxilla greatly enlarged. Fig. 169, different forms of scales, showing the great variation in size and form, the narrow ones running into a linear form, becoming hairs. The markings are also seen to vary, showing, their unreliable character as test objects, unless a single scale is kept for use.)
Lepidocyrtus. Abdominal segment unequal, with simple hairs and scales. Antennae long, four-jointed. Eyes eight in number on each side. (Fig. 170, L. albinos, an European species, from Hardwicke's "Science Gossip." Fig. 171, a scale. Two species live in New England.)
Podura. Abdominal segments subequal. Hairs simple, no scales. Antennae four-jointed, shorter than the head. Eyes eight in number on each side. Saltatory appendage of moderate length.
Achorutes. Abdominal segments subequal. Antennae short, four-jointed. Eyes eight in number on each side. Saltatory appendage quite short.
Figure 172 represents a species of this genus very abundant under the bark of trees, etc., in New England. It is of a blackish lead color; a, end of tibia bearing a tenant hair, with the tarsal joint and large claw; b, spring; c, the third joint of the spring, with the little spine at the base; figure 163, the supposed ovipositor; a, the two blades spread apart; b, side view. The mouth-parts in this genus are much as in Tomocerus, the maxillae ending in a lacinia and palpus.
The three remaining genera, Lipura, Anurida and Anura, are placed in the "family" Lipuridae, which have no spring. Lubbock remarks that "this family contains as yet only two genera, Lipura (Burmeister), in which the mouth is composed of the same parts as those in the preceding genera, and Anura (Gervais), in which the mandibles and maxillae disappear." Our common white Lipura is the European L. fimetaria Linn. (Fig. 173, copied from Lubbock). The site of the spring is indicated by an oval scar.
Figure 174 represents Anurida maritima found under stones between tide marks at Nantucket. It is regarded the same as the European species by Lubbock, to whom I had sent specimens for comparison. This genus differs in the form of the head from Lipura and also wants the terminal upcurved spines, while the antennae are much more pointed. The legs (Fig. 175) end in a large, long, curved claw. On examining specimens soaked in potash, I have found that the mouth-parts of this species (Fig. 176,) md, mandibles; mx, maxillae; e, eyes, and a singular accessory group of small cells, are like those of Achorutes, as previously noticed by Laboulbene. The mandibles, like those of other Poduras, end in from three to six teeth, and have a broad, many-toothed molar surface below. The maxillae; end in a tridentate lacinia as usual, though the palpi and galea I have not yet studied.
The genus Anura may be readily recognized by the mouth ending in an acutely conical beak, with its end quite free from the head and hanging down beneath it. The body is short and broad, much tuberculated, while the antennae are short and pointed, and the legs are much shorter than in Lipura, not reaching more than a third of their length beyond the body. Our common form occurs under the bark of trees.
For the reason that I can find no valid characters for separating these three genera as a family from the other Poduras, I am inclined to think that they form, by the absence of the spring, only a subdivision (perhaps a subfamily) of the Poduridae.
The best way to collect Poduras is, on turning up the stick or stone on the under side of which they live, to place a vial over them, allowing them to leap into it; they may be incited to leap by pushing a needle under the vial. They may also be collected by a bottle with a sponge saturated with ether or chloroform. They may be kept alive for weeks by keeping moist slips of blotting paper in the vial. In this way I have kept specimens of Degeeria, Tomocerus and Orchesella, from the middle of December till late in January. During this time they occasionally moulted, and Tomocerus plumbeus, after shedding its skin, ate it within a few hours. Poduras feed ordinarily on vegetable matter, such as dead leaves and growing cryptogamic vegetation. These little creatures can be easily preserved in a mixture of alcohol and glycerine, or pure alcohol, though without the glycerine the colors fade.
We have entered more fully in this chapter into the details of structure than heretofore, too much so, perhaps, for the patience of our readers. But the study of the Poduras possesses the liveliest interest, since these lowest of all the six-footed insects may have been among the earliest land animals, and hence to them we may look with more or less success for the primitive, ancestral forms of insect life.
[Footnote 9: Nicolet, in the "Annales de la Societe Entomologique de France" (tome v, 1847), has given us the most comprehensive essay on the group, though Latreille had previously published an important essay, "De l'Organization Exterieure des Thysanoures" in the "Nouvelles Annales du Museum d'Histoire Naturelle, Paris, 1832," which I have not seen. Gervais has also given a useful account of them in the third volume of "Apteres" of Roret's Suite a Buffion, published in 1844.
The Abbe Bourlet, Templeton, Westwood, and Haliday have published important papers on the Thysanura; and Meinert, a Danish naturalist, and Olfers, a German anatomist, have published important papers on the anatomy of the group. In this country Say and Fitch have described less than a dozen species, and the writer has described two American species of Campodea, C. Americana, our common form, and C. Cookei, discovered by Mr. C. Cooke in Mammoth Cave, while Humbert has described in a French scientific journal a species of Jupyx (J. Saussurii) from Mexico.]
[Footnote 10: The direct homology of these parts of the head (the occiput and the epicranium) with Perla, Forficula, etc., seems to me the best evidence we could have that the Podurae are not an independent group. In these most fundamental characters they differ widely from the Myriopods. I am not aware that this important relation has been appreciated by observers.]
[Footnote 11: As we descend to the soft, tube-like, suctorial (?) mouth of Anura, which is said not to have hard mouth-parts, we see the final point of degradation to which the mouth of the Thysanura is carried. I think that this gradual degradation of the mouth-parts in this group indicates that the appendages in these animals are not formed on an independent type, intermediate, so to speak, between the mandibulate and haustellate types, but are simply a modification (through disuse) of the mandibulate type as seen in Neuropterous insects.]
[Footnote 12: Lubbock considers that Papirius should be placed in a distinct family from Smynthurus, because it wants tracheae. Their presence or absence scarcely seems to us to be a family character, as they are wanting in the Poduridae, and are not essential to the life of these animals, while in other respects Papirius seems to differ but slightly from Smynthurus.]
[Footnote 13: Dr. Laboulbene has recently, and we think with good reason, separated Anura maritima from the genus Anura, under the name of Anurida maritima.]
HINTS ON THE ANCESTRY OF INSECTS.
Though our course through the different groups of insects may have seemed rambling and desultory enough, and pursued with slight reference to a natural classification of the insects of which we have spoken, yet beginning with the Hive bee, the highest intelligence in the vast world of insects, we have gradually, though with many a sudden step, descended to perhaps the most lowly organized forms among all the insects, the parasitic mites. While the Demodex is probably the humblest in its organization of any of the insects we have treated of, there is still another mite, which, some eminent naturalists continue to regard as a worm, which is yet lower in the scale. This is the Pentastoma (Fig. 177, P. taenioides), which lives in the manner of the tape worm a parasitic life in the higher animals, though instead of inhabiting the alimentary canal, the worm-like mite takes up its abode in the nostrils and frontal sinus of dogs and sheep, and sometimes of the horse. At first, however, it is found in the liver or lungs of various animals, sometimes in man. It is then in the earliest or larval state, and assumes its true mite form, being oval in shape, with minute horny jaws adapted for boring, and with two pairs of legs armed with sharp retractile claws. Such an animal as this is little higher than some worms, and indeed is lower than many of them.
We should also not pass over in silence the Centipedes (Fig. 178, Scolopocryptops sexspinosa) and Galley worms, or Thousand legs and their allies (Myriopods), which by their long slender bodies, and great number of segments and feet, vaguely recall the worms. But they, with the mites, are true insects, as they are born with only three pairs of feet, as are the mites and ticks, and breathe by tracheae; and thus a common plan of structure underlies the entire class of insects.
A very strange Myriopod has been discovered by Sir John Lubbock in Europe, and we have been fortunate enough to find a species in this country. It is the Pauropus. It consists, when fully grown, of nine segments, exclusive of the head, bearing nine pairs of feet. The young of Pauropus (Fig. 179) is born with three pairs of feet, and in its general appearance reminds us of a spring-tail (Fig. 180) as may be seen by a glance at the cut. This six-legged form of Pauropus may also be compared with the young galley worm (Fig. 181).
Passing to the group of spiders and mites, we find that the young mites when first hatched have but three pairs of feet, while their parents have four, like the spiders. Figure 182 represents the larva (Leptus) of the red garden mites; while a figure of the "water bear," or Tardigrade (Fig. 183), is introduced to compare with it, as it bears a resemblance to the young of the mites, though their young are born with their full complement of legs, an exception to their nearest allies, the true mites. Now if we compare these early stages of mites and myriopods with those of the true six-footed insects, as in the larval Meloe, Cicada, Thrips and Dragon fly, we shall see quite plainly that they all share a common form. What does this mean? To the systematist who concerns himself with the classification of the myriads of different insects now living, it is a relief to find that all can be reduced to the comparatively simple forms sketched above. It is to him a proof of the unity of organization pervading the world of insects. He sees how nature, seizing upon this archetypal form has, by simple modifications of parts here and there, by the addition of wings and other organs wanting in these simple creatures, rung numberless changes in this elemental form. And starting from the simplest kinds, such as the Poduras, Spiders, Grasshoppers and May flies, allied creatures which we now know were the first to appear in the earlier geologic ages, we rise to the highest, the bees with their complex forms, their diversified economy and wonderful instincts. In ascending this scale of being, while there is a progress upwards, the beetles, for instance, being higher than the bugs and grasshoppers; and the butterflies and moths, on the whole, being more highly organized than the flies; and while we see the hymenopterous saw-flies, with their larvae mimicking so closely the caterpillars of the butterflies, in the progress from the saw-flies up to the bees we behold a gradual loss of the lower saw-fly characters in the Cynips and Chalcid flies, and see in the sand-wasps and true wasps a constant and accelerating likeness to the bee form. Yet this continuity of improving organizations is often broken, and we often see insects which recall the earlier and more elementary forms.
Again, going back of the larval period, and studying the insect in the egg, we find that nearly all the insects yet observed agree most strikingly in their mode of growth, so that, for instance, the earlier stages of the germ of a bee, fly or beetle, bear a remarkable resemblance to each other, and suggest again, more forcibly than when we examine the larval condition, that a common design or pattern at first pervades all. In the light of the studies of Von Baer, of Lamarck and Darwin, should we be content to stop here, or does this ideal archetype become endowed with life and have a definite existence, becoming the ancestral form of all insects, the prototype which gave birth to the hundreds of thousands of insect forms which are now spread over our globe, just as we see daily happens where a single aphis may become the progenitor of a million offspring clustering on the same tree? Is there not something more than analogy in the two things, and is not the same life-giving force that evolves a million young Aphides from the germ stock of a single Aphis in a single season, the same in kind with the production of the living races of insects from a primeval ancestor? When we see the Aphis giving origin in one season to successive generations, the individuals of which may be counted by the million, it is no less mysterious than that other succession of forms of insect life which has peopled the globe during the successive chapters of its history. While we see in one case the origin of individual forms, and cannot explain what it is that starts the life in the germ and so unerringly guides the course of the growing embryo, it is illogical to deny that the same life-giving force is concerned in the production of specific and generic forms.