living specimens were exhibited to the Fellows; whilst from information received then and since, it seems that their appearance was general and simultaneous at a large number of places in the counties of Sussex, Kent, Surrey, and Middlesex. Naturally the first question that arose was, where did the creatures come from? And in reply to this there were not wanting persons who, connecting their appearance with the storm and the rain, boldly claimed for them a celestial origin, and well-authenticated instances of the descent of small fish and frogs from the clouds were adduced in support of the notion; whilst other persons gravely inquired whether they might not have been produced by electricity-an idea which, though at first sight absurd, certainly does not, upon reflection, seem to be surrounded by any greater difficulties than those of the more fashionable but less novel theories of spontaneous generation. Whilst endeavouring to investigate the subject, I thought it worth while to make inquiries whether anything special or peculiar in the condition of the atmosphere had been noted by meteorological observers; but with the exception of the unusual depth of the rainfall-registered at Kew as 727 inches, but at Steyning as no less than 2:44 inches,-I cannot ascertain that anything remarkable was anywhere recorded. But it is worthy of mention that sudden appearances of immense numbers of these worms took place in the years 1781, 1832, and 1845-on each occasion in the month of June, and immediately after thunderstorms with heavy rainfall; the prevailing opinions then being that they came from the clouds. Their appearance on June 15th, 1845, has been described at great length by the Rev. L. Jenkyns, in his "Observations on Natural History."* They were then found upon flagstones as well as on the earth, and were equally abundant upon shrubs and trees as high as examined-certainly 7 or 8 feet from the soil. It is not, however, my present purpose to occupy any more time either in following up these inquiries, or in entering into any speculations to account for the apparently anomalous circumstance of Entozoa being found in large quantities upon apple-trees and gooseberry-bushes; but it will, perhaps, be worth while, before going into any detailed description of what the microscope reveals of their structure, to state in as few words as possible what Natural History teaches us concerning them. They were first recognized as a distinct genus by Dujardin, who, in a memoir published in 1842,† minutely described them, and gave an account of what he considered to be their origin and habits. He was of opinion that they were chiefly parasites of the larvae of the cockchafer, which, he says, are many years coming to their full growth, and that they leave the bodies of their hosts only when

Pp. 303, et seq. † Annales des Sciences Naturelles, 1842.

arrived at maturity, and merely to lay their eggs, after which they speedily die. He accounts for their appearance after heavy rain by supposing that at such times the moisture stimulates the already sick larvæ to expel their parasites by contraction. But although this theory might in part explain their being found upon the ground, it does not so well account for their abundant presence on the tree-tops. These worms belong to the family Gordiacea, in the order Sterelmintha, of the class Entozoa. Formerly they were placed amongst the Nematoidea, in the order Cœlelmintha; but from the fact that they do not possess the distinctive characteristics of the last-named order, and do agree with those of the first-named, it is rather surprising that they should have been so long allowed to occupy a false position. In the family Gordiacea, the two British genera, Gordius aquaticus and Mermis nigrescens, bear so close a resemblance to each other that it is hardly to be wondered at that mistakes should often be made in identification; and it may be noted in passing that, with the exception of the descriptions already quoted from, the amount of written information concerning them is very meagre, owing, no doubt, to their very retired habits, and to the fact that they have not been discovered to be injurious, either directly or indirectly, to man or to his property. According to the various descriptions, the chief differences between the two may be stated as follows:-Gordius attains the length of 7 to 10 inches, Mermis from 4 to 6 inches. Gordius inhabits water or mud; Mermis is found in damp earth. In Gordius the oviduct is situated nearer to the posterior than to the anterior end of the body; in Mermis it is nearer to the anterior than to the posterior. In Gordius the head is much more abruptly rounded than is the case with Mermis; and, by error, in SCIENCE-GOSSIP, vol. i., p. 197, the tail of the female Gordius is stated to be bifid, whereas male is intended, as I am since informed, whilst that of the female Mermis is certainly simple, terminating in a rounded angle, as shown in the diagram. What sort of caudal appendage may be possessed by the male Mermis I am unable to state, since the whole of the fifty or sixty specimens in my possession belong to the female sex. Gordius is also of a much darker colour than Mermis; but both are developed in the intestines of insects, who find the 'ova and swallow themdoubtless afterwards wishing they had not. On the evening of June 3rd I received by post a small box full of these worms from a friend at Bognor, the letter which accompanied them stating that they had been found in great numbers that morning in the garden after the thunderstorm, chiefly depending in the manner already alluded to, from the leaves of the apple-trees. Specimens were also found upon asparagus, and on bushes and shrubs. On turning them out of the box, I found them to be quite dry

of force required to tear them from each other's folds. In colour some were a pale yellow; but the majority were more or less longitudinally streaked with brown, in some cases approaching to black. On placing one of them in water, it speedily began to untwist itself, and to writhe about in a manner strongly suggestive of returning animation; but although it is said that Gordius aquaticus will come to life again and swim away, after having been dried up for weeks, I am quite sure that these movements on the part of the many specimens of Mermis examined were merely the result of the relaxation of their stiffened bodies, consequent upon the absorption of the fluid in which they were immersed, the motion entirely ceasing as soon as the last trace of shrivelling had disappeared. The absorption of the water appeared to take place almost entirely through the substance of the skin; and it is stated that in their natural condition they obtain their nutriment in a similar manner. When thoroughly moistened, their bodies became naturally distended, cylindrical, transparent, and pliable in a remarkable degree, and so elastic that they bore stretching to much beyond their natural length without breaking asunder. On placing them under the microscope, upon moistened slides, I found that the dark colour of most of the specimens was due to the presence of large numbers of clear brown ova, which, in many instances, filled

the body from within inch of the head to inch from the tail, no fewer than 7,200 of them having been counted in the first one taken under examination. In length the worms varied from 3 to 5 inches, and in breadth or diameter from to inch, excepting at the extremities. The tail ended in a somewhat curved and rounded point, and there was no posterior aperture to the intestinal canal. From a distance of about inch from the head the body gradually tapers down, until it terminates in a slight rounded enlargement, just behind which there is a small, ill-defined, red spot; the diameter of the head in most cases does not exceed inch. Whether this worm has any mouth or not appears to have been hitherto a matter of some uncertainty, for in works where its characteristics are given I find it frequently stated, "Mouth none, or very indistinct;" and from the examination of nine out of ten mounted specimens, it was impossible to decide the question with any certainty; but in the tenth I was delighted to find that the structure of the mouth was shown in a remarkably clear and beautiful manner; for although this slide, as a specimen of mounting, is anything but what it ought to be, the head is more perfectly shown than in any former instance. From the examination of this, I think it may be determined that the creature is furnished with at least two very minute circular mouths or suckers, one on each side of the head, about 90° apart, or 45° on either side of the terminal extremity, from each of which a cone-shaped tube extends towards, and at its base joins, the alimentary canal. There is also some reason for suspecting the existence of one or more additional mouths. The body is filiform and cylindrical, its integument being perfectly transparent, homogeneous, very elastic and tough, and seemingly of a gelatinous nature. It absorbs water with great facility, undergoes no perceptible change from the action of sulphuric acid, but is instantly dyed brown by a solution of iodine. Its effect upon polarized light is very slight, unless in a state of tension, when it becomes brilliant, and exhibits beautiful graduating colours with selenite. The most noteworthy appearance connected with it is that it is delicately marked with an immense number of strim, which run spirally round it from end to end, preserving their parallelism throughout, their distance apart scarcely exceeding o inch. These markings are best seen when the worm is freely floating in fluid, and has not been subjected to pressure. (The specimen exhibited under the microscope in the room was placed in a glass cell containing water only, and in which it had been for more than two months without undergoing any perceptible change.) Whatever may be the nature of these markings, they seem to indicate the secret of the creature's climbing powers, and to confirm the opinion that it ascends the stems of shrubs by a winding spiral motion.

Next within the integument, and between it and the alimentary canal and ovary, are what appear to be two tubes or cords, which may possibly constitute the nervous system. These are well seen in polarized light. Whether there are two ovaries, or only one extending nearly the length of the body, I have not been able clearly to determine; but from the examination of the parts immediately adjacent to the oviduct, and from the fact that an incision made through the integument on one side of the vulva only caused ova to float out from that half of the body, I am inclined to believe that there are two distinct ovaries, as in the case of the common Ascaris. The ovaries appear to consist of fibrous tissue, very different in appearance and structure from that of the outer integument-a difference which becomes strikingly visible by the action of re-agents. Schultze's test, which produces no effect whatever upon the integument, changes this tissue immediately from its natural pale yellow colour to a deep crimson. When a worm has been immersed in water sufficiently long for its body to have become naturally distended and pliant, it should be cut in two with the scissors, and on pressure being applied to the extremity, and steadily continued along towards the cut end, the whole of the contents of the body will be forced out from the integument without any apparent injury to either. Treatment with acetic acid will render it easy to separate the fibres, or a drop of syrup and a drop of sulphuric acid added to it will change them to the deep red colour already referred to. But perhaps the greatest amount of interest may be said to attach to the ova themselves, which, from their great number and conspicuous colour, must immediately attract the attention of the most casual observer. The number in the different worms which I have had under the microscope I found to range from a few score to upwards of 10,000; in colour they are a clear transparent brown, and in shape slightly oval, having a major diameter of inch, and a minor of o inch. They may readily be obtained for examination, either by pressing out the contents of the body in the manner above described, or by placing the body of the worm in water, bending it nearly double, and then cutting it half-way through with a sharp-pointed dissecting knife; the ova will then be found slowly but freely to float out through the incision. A small quantity of acetic acid added to the water will be found to hasten the process, and I will also be of further service in clearing the ova from certain granules of matter by which they are frequently surrounded. On carefully examining them for the first time, I found that each one was enclosed in a delicate, colourless, membraneous sac, the opposite ends of which were slightly elongated, and furnished with two fine filamentous appendages, fringed or ciliated at their free ends. It is however rather remarkable that nearly all the ova of the

a, b, perfect ova. c, ruptured sac. d, ovum escaped, x 280. The sacs containing the ova were filled up with a fluid, the nature of which I have been unable to determine. What may be the purpose of the filaments appears to be a question of some interest; and it has been suggested that, inasmuch as the ova are found and devoured by various insects, within whose bodies they undergo development, possibly the filaments may have a use as a means of attachment, by which the ova are prevented from passing out of their hosts before coming to maturity. But be this as it may, I have observed that by a comparatively slight amount of pressure, the sac is ruptured and the ovum escapes. It is also further to be noted that in every instance of this kind the sac has broken asunder in the same direction and manner, namely, in the circumference of its minor diameter, thus separating it into two equal parts, each of which in shape bears a curious resemblance to a round-topped smoking-cap with its tassel. The rupture of the sacs was in all probability due to the compression of the contained fluid, so that it would be unfair to infer from this only that an insect would swallow the ovum alone without its envelope; yet I cannot but regret that my endeavours to clear up this point have not been attended with better success. With this end in view, I have for some days past kept an earwig in a closed glass trough in which I had placed some of the perfect ova; but up to the time I left home this evening they remained untouched, although the insect has had nothing to eat for nearly a week; and having been caught in a London scullery, it is scarcely probable that its aversion arises from any previous experiences of the effects of swallowing the ova of Mermis nigrescens.* Surrounding the ovaries, apparently in contact with the ova, and occupying the spaces between them, is what appears-when seen through the integument by transmitted lightto be a quantity of milk-white flocculent material,

* To save it from death by starvation, the earwig was set at liberty a few days after, the ova remaining untouched.

which I take to be alimentary matter; it freely floats out with the ova when an incision is made, or it may be obtained directly from a cut portion by

Fig. 224. Bi-caudate Ovum, x 575.

pressure. Examined under a 1-inch objective,' it is seen to consist of semi-transparent granules or corpuscles; and it appeared of some importance to endeavour to ascertain what they consisted of-not merely from curiosity as to the worm's diet, but as tending to show whether or not they might be regarded as injurious to the vegetable produce of those gardens where they exist in such numbers. The result of sundry experiments seems, however, clearly to show that this granulated matter is neither of animal nor vegetable composition, inasmuch as it remained unchanged by the action of Schultze's test and of iodine. By adding sulphurie acid to a portion already treated with iodine, very minute isolated patches only gave a purple reaction, seeming to indicate the presence of cellulose; but strong sulphuric acid acted powerfully upon it, disengaging small bubbles of gas. Finding this to be the case, I allowed it to stand aside for a couple of days; and at the end of that time I found floating in the liquid numerous bundles of the wellknown acicular crystals of sulphate of lime. For preservation as microscopic objects, entire specimens of Mermis may be readily mounted, freely floating in cells filled with water or glycerine. When intended to be viewed as transparent objects, they should be thoroughly saturated with water, then placed in the required position between two glass slides, and allowed to dry under pressure, after which they can be mounted in the usual manner in glycerine jelly or pure glycerine, under a glass cover only. With the ova alone greater care is necessary; and to avoid the results of pressure they should be protected by a very shallow cell, in which glycerine is undoubtedly the best medium for their preservation. All my attempts with balsam have turned out badly; for though free from bubbles, the sacs have in every case been broken, and the escape of the contained fluid has caused a blurred appearance round all those of the ova which were not completely isolated.

THE DRAGON-FLY.

BY A. S. PACKARD, JR., M.D.

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 twelvemonth, 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 does 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 larvæ 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's 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, since our fiend of the air is a poor pedestrian.

Its gleaming wings are, however, beautiful objects. They form a broad expanse of delicate parchmentlike 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 colours. 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 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 Libellula 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 antennæ. Seen from beneath, instead of the formidable array of jaws and accessory organs commonly observed in most carni

vorous larvæ, 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 endeavouring 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 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 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 trachea 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 or five triangular horny valves, 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. This is then suddenly expelled by a strong muscular effort.

In the smaller genera, Agrion, Lestes, and Calopteryx, the respiratory leaves, called the tracheary, or false-gills, are not inclosed within the body, but form three broad leaves, permeated by trachea, or air-vessels. They are not true gills, however, as the blood is not aërated in them. They only absorb air to supply the trachea, which aërate 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 easy 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 Libellulida may be always known from the Eschnidæ by the shorter, deeper, and more robust form, and generally by their thick clothing of hair.”

The pupa scarcely differs from the larva, except