Through a pocket lens

In this chapter we shall take examples from two Classes—the Arachnoi´dea and the Myriap´oda. To the first-named Class belong also the Scorpions, which, with the Book Scorpions, the Harvestmen, and some others, may be neglected here. This will leave us only the Spiders and Mites to deal with.

Every one knows a Spider when he sees one, though not every one can give offhand a definition that shall include the whole Order. Let us endeavour to express their characters in simple terms, keeping in mind the definition of head, thorax, and abdomen in Chapter II. In Spiders the head and thorax are joined together in one unsegmented portion, called the cephalothorax, and this is connected with the abdomen, which is also unsegmented, by a more or less slender stalk or peduncle. So that while Insects have three regions, Spiders have but two. We may express the difference thus:

The cephalothorax bears six pairs of appendages (Fig. 48A). Taking these in order, there are—

Breathing is carried on by chambered air-tubes or lung-sacs, and in all our British Spiders (with the single exception of the native Trap-door Spider, which, by the way, does not make a trap-door) there are also air-tubes resembling those of Insects. The lung-sacs open to the external air by stigmata (st) on the abdomen, while the ordinary air-tubes open near the spinnerets (sp), the organs employed in the production of the silky threads from which are formed webs, nests, egg-bags, and ropes. By means of these threads, spiders drop from their webs to the ground, construct flying bridges from one point to another, and even in some sort travel through the air.

Spiders live upon the juices of their prey, which are drawn up into the stomach by means of a suctorial apparatus at the end of the gullet. The young, when they leave the egg, resemble their parents in all respects but size—that is, they undergo no metamorphosis.

The eyes of spiders are simple, and six or eight in number. These vary much in size and relative position, and furnish characters of great importance in classifying species. Those of the Hunting Spiders, which make no web, but pursue or spring upon their prey, are usually arranged in three rows; while those which make webs for the capture of prey have the eyes in a double row. In all cases they are on the front part of the upper surface of the cephalothorax.

The Common Garden Spider (Epei´ra diade´ma) is a very good subject, and there can be no difficulty in procuring any number of specimens. The smallest garden will be sure to yield a plentiful supply; and even if we have no garden, a very superficial search among the hedgerows will give us as many as we can possibly want. Every one knows this spider, and the beautifully regular web which it makes. First of all, what one may call the outline of the web is spun—strong threads stretching from point to point, to which are attached lines radiating from a common centre. This may be represented diagrammatically by drawing a circle and producing radii from the centre to the circumference in all directions, or by making a rectangular figure and drawing lines to the boundaries from the point where the diagonals intersect. It must not, however, be supposed that the outline of the web is of a regular form. In this respect the spider adapts itself to circumstances, and spins a greater or less number of supporting threads, as may be necessary.

Then the spiral is made (Fig. 49) from the centre to the circumference. The first few turns are of the same character as the radial lines; but all the rest of the short lines forming the spiral, and connecting the radial lines, are coated with a viscid secretion, which is the essential part of the snare; for the victims are really limed like birds on a twig, not entangled in the threads. It is well to test the character of the different parts of the spiral, not only by touch, which is convincing enough, but with pocket lens. Our low powers will not give such results as are shown in Fig. 50, but we shall have no difficulty in distinguishing the sticky parts from those not coated with the secretion.

It may be doubted whether all the Spiders of this genus make the spiral in the same way, for observers differ in their description of what they have seen. Some say that a non-adhesive spiral from centre to circumference is first made, and that the spider then moves ‘in a closer spiral from the circumference inwards, biting away the former spiral, replacing it by another, which is viscid and adhesive[29].’ Dr. Butler, on the other hand, who ‘watched spiders for months together, petting, feeding, and trying experiments with them every morning,’ after describing the making of the first and non-adhesive part of the spiral, says, ‘This line is not carried to the boundary, but at some distance from the centre a second is commenced, formed of extremely viscid silk, upon which the gummy secretion is distinctly visible, with the aid of a lens, in the form of closely approximated globules of amber-coloured glue. It is said that when the viscid lines are completed the spider cuts away the unadhesive lines, but this I have never observed[30].’ My own observations lead me to believe that Dr. Butler is correct in his description. Though I have often watched, I have never seen a spider ‘biting’ away any part of its web, nor would the falces appear to be adapted for such an operation. They are piercing, not cutting, weapons.

The spider may be watched at leisure, if put into a bottle of moderate size, the top of which should be covered with muslin or calico to prevent escape. Here it is fairly easy to bring the pocket lens into play, and to distinguish the different parts of the animal. The eyes, and their arrangement, should be particularly noticed.

Blackwall, in support of the position that in making their webs spiders are guided by touch rather than sight, says, ‘Various species, when confined in spacious glass jars placed in situations absolutely impervious to light, construct nets which do not exhibit the slightest irregularity of plan or defect of structure[31].’ My specimens have always been kept in the light, and in small bottles rather than spacious jars, but I have never seen spiders attempt to make a geometrical web under such conditions.

A bottle which for some months served as a prison-house for a Garden Spider now stands on my writing-table. Its sides are marked by hundreds of ‘anchorages’—but the threads cross and recross, forming in some parts a kind of sheet, and in others a tangled mass. Some of these threads must have been covered with viscid secretion, for flies were limed, and so fell a prey to the spider. Their dried skins are dotted about among the threads, and the spider itself perished long ago from cold. But I keep the bottle as a curiosity, to show that these spiders do not always make geometrical webs.

When one has a Garden Spider in a bottle, it may be observed to practise a curious and very effective method of disabling its prey. If a bluebottle or any other large fly be dropped and entangled among the threads, the spider will envelop it in a sheet of web. This is how Blackwall describes the operation: ‘Causing the victim to rotate by the action of the third pair of legs and the palps, the first pair of legs also being frequently employed in a similar manner, they extend the spinners laterally, and applying to them alternately the sustentaculum of each posterior leg, they seize and draw out numerous fine lines in the form of a fillet, which they attach to their revolving prey, and thus involve it in a dense covering of silk from one extremity to the other. By means of this stratagem they are capable of overcoming formidable and powerful insects, such as wasps, bees, and even large beetles[32].’

The operation does not occupy much time; in a very few minutes the fly is swathed in a silky covering as completely as an Egyptian mummy in its linen folds. Of course resistance, much less attack, is out of the question, and when it is thus rendered powerless for harm the spider proceeds with its meal.

The sustentac´ulum—or support—is a strong movable spine near the end of the tarsus, on the under side of each of the last pair of legs. These spines act in opposition to the claws, and thus these animals are enabled to hold with a firm grasp such lines as they have occasion to draw from their spinners with the feet of the hind legs, and such also as they design to attach themselves to.

With regard to this method of swathing prey, Hudson[33] says of an Argentine spider, ‘that its intelligence has supplemented this instinctive procedure with a very curious and unique habit. The Pholcus, in spite of its size, is a weak creature, possessing little venom to dispatch its prey with, so that it makes a long and laborious task of killing a fly. A fly, when caught in a web, is a noisy creature, and it thus happens that when the Daddy longlegs—as Anglo-Argentines have dubbed this species—succeeds in snaring a captive, the shrill outrageous cries of the victim are heard for a long time—often for ten or twelve minutes. This noise greatly excites other spiders in the vicinity, and presently they are seen quitting their webs and hurrying to the scene of conflict. Sometimes the captor is driven off, and then the strongest or most daring spider carries away the fly. But where a large colony are allowed to continue for a long time in undisturbed possession of a ceiling, when one has caught a fly he proceeds rapidly to throw a covering of web over it, then, cutting it away, drops it down and lets it hang suspended by a line at a distance of two or three feet from the ceiling. The other spiders arrive on the scene, and after a short investigation retreat to their own webs, and when the coast is clear our spider proceeds to draw up the captive fly, which is by this time exhausted with its struggles.’

In this connexion Hudson notes that spiders are attracted by the sound of the vibration of a string or wire, thinking it made by an insect that has been caught; and he says that the stories of tame spiders are founded on a misunderstanding of the motive that brings the animal down. We may well doubt if spiders are attracted by music, but that some spiders possess a sense of hearing, or something analogous thereto, seems to be proved by the existence of stridulating organs in certain members of the group.

Two other points remain to be noted. The feet should be examined, for their structure throws some light on the way in which the Garden Spider runs so securely to and fro on the radial lines. One of the legs of a dead specimen should be detached, and its armature of spines and hairs noted. The foot is armed with three stout claws, which are pectinated—that is, toothed like a comb, and beneath them are smaller ones, sometimes described as toothed hairs. It will be easy to understand what a secure foothold these claws give the animal as it runs backwards and forwards over the radial lines; for if the web be shaken by the wind or designedly its owner can take a firm hold with each foot, and thus have eight separate points of attachment. An inch hand lens is quite sufficient to give a general idea of the hairy and spinous clothing of the legs and the position of the claws; but to see the teeth a higher power—a half-inch—will be necessary.

It is a good plan to choose a freshly killed specimen for the examination of its spinnerets. If the spider is laid on its back in a glass dish, gentle pressure on the abdomen away from the cephalothorax will cause the material secreted by the spinning-glands to ooze out. This, however, cannot be done if the specimen has been for some time in spirit. We shall be able to make out six tubes (four of them larger than the other two) grouped round the anal aperture; but, for the present, we must take for granted the fact that these are made up of a number of smaller tubes, so that the end of each spinneret is not unlike the rose of a watering-can. A good half-inch will give some indications of this rose-like appearance.

The Jumping Spider (Sal´ticus sce´nicus) belongs to a family the members of which make no web or snare for the capture of prey, but trust for their food-supply to their skill in stalking flies and other insects, which they capture by a sudden spring. It is from this habit that the type-genus and the family have received their scientific and popular names.

The common British species is extremely abundant, and wherever flies are plentiful these spiders will not be very far off. This is the case not only in the country, but also in London and other large towns. It is a noticeable spider from its coloration—black marked with white. The eyes are eight in number; though the artist in our illustration has only represented four. The centre two of the front are the largest of all, and have been compared not inaptly to bull’s eyes. Two others are placed on each side of the cephalothorax, so that the eyes form, roughly, three sides of a square, and the central eyes in the lateral lines are the smallest. We may represent them thus , while the eyes of the Garden Spider are disposed in this fashion .

It requires some little practice to detect the eyes of spiders and to remember their position in the different genera, but by examining every spider met with, and consulting some handbook to the group, one will soon be able to determine the commoner British species.

With a couple of needles we may remove the falces (Fig. 55) for examination; and there is no difficulty in mounting them, as shown in the cut, on a piece of card, so that they may be compared with the same weapons in other species. For example, the falces of the Garden Spider differ from those of the Jumping Spider in that they are short and stout, and the teeth on the basal joint are more in number.

The following account of the habit of this spider in capturing prey is from Kirby and Spence’s Introduction to Entomology (ed. 1870, p. 453):—‘When these insects spy a small gnat or fly upon a wall, they creep very gently towards it with short steps, till they come within a convenient distance, when they spring upon it suddenly like a tiger. Bartram observed one of these spiders that jumped two feet upon a humble-bee. The most amusing account, however, of the motions of these animals is given by the celebrated Evelyn in his Travels. When at Rome, he often observed a spider of this kind hunting the flies which alighted upon a rail on which was its station. It kept crawling under the rail till it arrived at the part opposite to the fly, when stealing up it would attempt to leap upon it. If it discovered that it was not perfectly opposite, it would immediately slide down again unobserved, and at the next attempt would come directly upon the fly’s back. Did the fly happen not to be within a leap, it would move towards it so softly, that its motion seemed not more perceptible than that of the shadow of the gnomon of a dial. If the intended prey moved, the spider would keep pace with it as exactly as if they were actuated by one spirit, moving backwards, forwards, or on each side without turning. When the fly took wing, and pitched itself behind the huntress, she turned round with the swiftness of thought, and always kept her head towards it, though to all appearance as immovable as one of the nails driven into the wood on which was her station: till at last, being arrived within due distance, swift as lightning she made the fatal leap and secured her prey.’

This spider employs a clever precaution against falling, when about to spring upon its prey. It applies the end of the abdomen to the surface on which it stands, and opening its spinnerets, makes an ‘anchorage’ (Fig. 56). Then, by the act of springing, it draws from the spinnerets a line attached to the spot from which it started. This line is strong enough to support the spider in case it misses its prey.

The foot of the Jumping Spider is extremely interesting, and shows a very ingenious arrangement, by means of which the animal can run with difficulty on smooth polished upright surfaces, or retain its footing when it alights on such surfaces after a spring. We can see this arrangement in Fig. 56. Just behind the claws is a bundle of coarse hairs, technically called a scop´ula, or little brush. From these hairs adhesive matter flows, and in this fashion the spider literally sticks on. With this brush of hairs may be compared the tarsal cushions of many flies, and the adhesive hairs of Dytiscus and other beetles (see Chap. II)—though these last have a different function.

Diving Spiders (Argyrone´ta aquat´ica) are especially suitable for our purpose. They are very common in most ponds, and in some places are so abundant as to be almost a nuisance to the collector who is in search of other things. Three of them are represented in Fig. 57. One is swimming; another is just entering the bell-shaped web under water; and the third is just climbing out of the water on to the broad floating leaves of the water crowfoot.

De Geer’s account of these spiders is extremely interesting[34], and we may verify it for ourselves, for these creatures may be kept without any trouble. They certainly agree, when a number are kept in captivity, much better than do other spiders. De Geer kept several in the same aquarium, and says that when they met they felt each other with their palps, and opened their falces, but he never saw them do any harm to each other. I have kept them under similar conditions with the same result.

He tells us that these spiders spin under water a cell of strong, close, white silk, the shape of which he compares to a skull-cap, the half of a pigeon’s egg, or a diving-bell. In September, 1736, he first became acquainted with these creatures, and kept one in an aquarium for four months. It made its cell against the side of the aquarium, and the top of it rose above the surface of the water. (This was due to its being inflated. The web was not spun above the surface.) The walls of the cell were very thin, but it was filled with air, and the spider was resting inside, head uppermost, with its legs pressed against the body.

About three months later he found that the mouth of the cell was closed, and the spider was comfortably settled in its winter quarters. When pressure was applied the cell burst and the air escaped, mounting up to the top in bubbles. The spider made its way out, and took an Asellus that was offered, and made a meal of it.

De Geer then came to the conclusion that these cells under water were constructed for the purpose of affording the spider a retreat when the water was frozen over, so that they could not come to the surface for a supply of air. He found, however, by observation, that they were also made in summer by both sexes. In a cell of this kind the female deposits her eggs—from eighty to a hundred in number, enclosed in a cocoon of white silk—and keeps guard over them, with her head defending the entrance to the cell.

He succeeded in finding out the method by which the Diving Spider fills its cell with air. He noticed that when the creature was moving about in the water, its body was covered with a layer of air, and that this air was renewed from time to time when the animal came to the surface and raised its abdomen above the water. Loaded, so to speak, with air in this fashion, the spider descended, and entered the cell backwards, leaving an air-bubble. Having repeated this several times, at last she removed all the water from the cell, introducing in its place an equal quantity of air.

It is very easy to watch the Diving Spider making its dwelling under water, and filling it with air. First of all the web is woven in a bell or thimble shape between the sprays of water-weed, or against the bottom or side of the aquarium. It is curious to notice how practices that must be necessary when the creature is at liberty are continued in captivity where they are useless. A web constructed in running water, or even in a pond or ditch, is liable to be swept away or to be emptied of air by a very slight current, so its owner has recourse to a system of guys and supporting threads, which are not required when the spider is safely housed in a small aquarium. Nevertheless, the guys are made. In an eight-ounce bottle I have now a male Diving Spider, which has lived there for about seven months. Its cell is made between the whorls of a spray of milfoil, and guy threads have been carried to no less than five whorls—two above and three below the opening. Now that it is filled with air, the cell gleams in the water like a great bubble of quicksilver. The air may be expelled by shaking or tilting the bottle, and if the web be not damaged the spider will generally refill it with air, though sometimes it prefers to make a new dwelling. Fig. 58 shows the cell of a Diving Spider; the white lines represent supporting threads attached to the water plants.

In examining dead specimens we shall find that, contrary to what is usual, the male exceeds the female in size. I have a slide of a male, with the legs spread out before and behind, and the measurement from the claws of the first pair of legs to those of the fourth pair is 1¾ inches. The body is ¾ inch long. The whole surface is more thickly clothed with hair than is the case with other spiders, and the reason for this is obvious. This hairy body-covering serves to carry down into the water a layer of air, and the fringe of hair on the legs makes them efficient swimming organs.

The Order of Mites will yield us subjects for our pocket lens. Mites are related to Spiders, but form a distinct Order. Like the Spiders, some are aquatic, though the most of them live on land. Many are parasitic, during the whole or part of their lives subsisting on the juices of their hosts: the food of others consists of organic débris, and these seem to be of benefit to man, since they act as scavengers. If we turn to page 96 we shall there find noted the points of difference in the arrangement of the main divisions of the body in Insects and in Spiders. In Mites the distinction between the cephalothorax and abdomen is lost, and the body is more or less oval or globular. In the perfect forms there are eight legs; but some, in their earlier stages, have only six. The mouth may be adapted for biting, though it is usually suctorial. In the Cheese Mites and some others breathing seems to be carried on through the skin, for there are no air-tubes; but in most Mites air-tubes, with two stigmata, are present.

If we take a dip with the collecting-net in almost any pond we shall be pretty sure to capture some specimens of Water Mites of the genus Hydrach´na, easily recognizable by their bright coloration, their eight swimming legs thickly fringed with hair, and their unceasing activity. They may be kept in a bottle, or other small vessel, with some water-weed, and will forage for themselves. In Fig. 59 we shall see the points we have to look for in examining a Water Mite with a pocket lens. There should be no difficulty in making out in the specimen all the details shown in the cut.

It may be that they will breed: if so we should avail ourselves of the opportunity of watching their development. Their life-history is somewhat curious, and is specially interesting from the fact that while Swammerdam had some faint perception of the true meaning of what he saw, De Geer, writing a hundred years later, drew entirely wrong conclusions from similar observations. It was left for Dugès to clear up the matter in the Annales des Sciences Naturelles, 1834. Before summarizing the account of the French naturalist it may be well to quote what Swammerdam and De Geer have said on the subject:—

‘There is nothing more remarkable in this insect [the Water Scorpion] than that it constantly appears covered with a prodigious number of nits of different sorts and sizes, though perhaps we may with more reason consider them as so many little creatures, which live and grow by sucking the Scorpion’s blood. These are somewhat of an oblong figure, approaching to round, and have a shining, and as it were bloated, surface, without any of the rings observable in most insects. The neck is oblong and shaped like a pear, with the small end sticking in the Scorpion’s body. The colour of this insect is a mean between that of vermilion and purple; and when it is pretty well grown there appears within it an elegant transparent spot or particle (Fig. 59).

‘This spot or particle induced me to consider with more attention this minute and hitherto unregarded insect, and even to undertake the dissection of it. But who would imagine that on this examination it should prove a perfect and surprising insect? This is, however, a certain fact; and thus in that infinite variety of works, by means of which God is pleased to make Himself known to us, we ever meet with new matter of admiration and astonishment.

‘This little creature being extracted from the shell that covered it, looks like a young spider before it has left its egg. On the fore part is the head (Fig. 43D, a) and on its head are the eyes, b: under the eyes are placed its little legs elegantly coiled and folded, c c; but they appear much more distinctly on turning the insect on its back, d d; and in this situation also it best appears with what art these legs are laid up in the shell, and all are covered with hair. The colour of this little creature is, as I have already observed, a mean between that of vermilion and purple; and this colour shows itself through the coat or shell, which is transparent. I cannot determine to what species of insects this is to be referred; nor can I say to what size it grows, or by what kind of creature it is thus deposited on the Water Scorpion in the form of an egg, there to receive life and growth. Nevertheless, I cannot but look on the discovery I have made as very interesting, since it proves that there are in the nature of things eggs which acquire a sensible growth by an entraneous nourishment, unless perhaps some naturalist should choose to consider this as a complete insect, rather than as an egg; nor shall I strenuously oppose his opinion, seeing that, in all cases, the egg is in reality no other than the insect itself, which remains in that state till it has acquired sufficient strength to break its prison, and live without such a covering[35].’

Having quoted Swammerdam, let us see what De Geer has to say on the subject:—

‘On the body and legs of many aquatic insects, such as Dytiscus and Water Scorpions, may be frequently seen little oval, seed-like bodies, of a bright red colour, firmly attached, and, as it were, implanted in the skin, by a little stalk. I have had Water Scorpions with the upper surface so covered with these red bodies that there was scarcely a vacant space on the skin. They are most frequently to be seen in the spring; but the insects on which there was such a great number did not live long with me. Having crushed some of these seed-like bodies, I found them filled with red liquid matter. I am convinced, by experiment, that they are the eggs of Water Mites, since there came out of them little red Mites with round bodies and long legs, which swam about with great swiftness.

‘These red Water Mites, then, attach their eggs to the bodies and legs of larger aquatic insects, and there they remain till the young are hatched. And since we find eggs of many different sizes, we may be sure that they grow and increase in size, doubtless owing to a certain nutritive juice which passes from the body of the insect into the egg. Hence it is, as I have seen myself, that Water Scorpions loaded with these eggs become weak and feeble, because they are obliged to furnish their hangers-on with nourishment from their own bodies. Moreover, these eggs appear to cause the Water Scorpions some irritation or uneasiness, since I have often seen them rub with their feet those parts of the body where the eggs were; and perhaps they did this with the view of rubbing them off, but they were too securely fastened[36].’

Dugès watched the development of the common Red Water Mite (Fig. 59), and tells us that towards the end of May the females deposit their eggs in the leaves of pondweed, which they puncture with their beaks. The larva (Fig. 60), red in colour, with six legs, is free-swimming, and has a large beak, which looks like a great head, and terminates in a narrow mouth. It is not known how long this larval stage continues; but in the next stage (Fig. 61) the Mite becomes parasitic on aquatic beetles and bugs, fastening its beak into the body of its host, from which it derives its nourishment. The legs and palps are often retracted or absorbed, so that it is not difficult to understand how it was Swammerdam and De Geer took these parasitic nymphs to be the eggs of the Mite. During their parasitic condition they increase considerably in size, at last emerging as adult eight-legged free-swimming Mites. It was just before the emergence of the Mite that Swammerdam examined the parasitic nymph, for he figures the ‘insect,’ which he extracted from the egg, as having eight legs (Fig. 43D).

I once found a Water Mite in the body of a Dytiscus[37]. I was breaking up the beetle, and had removed the elytra and the wings. I only wanted the external skeleton; so a slit was made between the plates of the dorsal and ventral surface, and the intestines removed. The Mite was embedded in the fat-body. I could find no mention in the literature of Beetles or Mites of any similar occurrence; and should scarcely have mentioned it here, had I not been unexpectedly confirmed by my friend Mr. G. E. Mainland, F.R.M.S., who once had a similar experience, and who kindly allows me to quote from a letter he sent me on the subject:—

‘I am sorry to say I can find no documentary evidence as to the Arachnid I found embedded in the tissues of Dytiscus, but a good deal has come back to my recollection. On removing the right elytron and slitting up the dorsal surface, I found it in the tissue close up to the thorax. I cannot recollect what ultimately became of it, after I had shown it to friends at the Hackney Microscopical Society.... I know that I carefully measured the Hydrachna (which was abnormally large) and its relative size to that of its host, and made a comparison in a lecture (to the Senior Band of Hope at St. Michael’s, Hackney) of a man with a creature as large as a guinea-pig under his shoulder-blade.’

The occurrence of the Mite inside the Beetle was, of course, quite exceptional. It probably found its way in through one of the abdominal spiracles.

The Beetle Mite (Gam´asus coleoptrato´rum) (Fig. 62) is extremely common, and is parasitic on the Dung Beetle and on the Humble Bee, so that in order to examine the parasite we must capture the host. There can be no difficulty about this, for Dung Beetles and Humble Bees are plentiful enough. This Beetle Mite, apparently, does not infest other species of beetles. I have kept the Devil’s Coach Horse in a bottle with the common Dung Beetle for some months, and though the latter swarmed with these parasites, they never left their host for the other beetle. Even when removed by means of a small brush from one beetle to the other, they left the Devil’s Coach Horse of their own accord, and soon made their way back to the Dung Beetle.

These parasites, with their host, came into my possession in a strange way. A friend, who knew my hobbies, told me that he had managed to procure for me some young beetles just born. I ventured to suggest that beetles were not born as beetles, but in quite a different shape. My suggestion was received unsympathetically, and I was told that I should alter my opinion when the creatures were sent me. But I did not. The box contained a Dung Beetle, over which were swarming scores of these little Mites, and I had some difficulty in convincing the gentleman who sent them to me that these Mites were not the young of the beetle.

We should compare this Beetle Mite with the Water Mite, and notice the difference in the mouth parts and the legs, which have a large pad between the claws.

We may find another Beetle Mite, closely allied to this species, on the Devil’s Coach Horse, and some of its near relations. This Mite was also known to De Geer[38], whose remarks upon it are worth quoting, in a condensed form.

He found a beetle covered with these Mites, and on examining them with a hand lens saw that they were attached to their host by a long thread or stalk, which came from the posterior end of the body. Several Mites, he tells us, were joined together by one thread which fastened them all to the beetle; and he came to the conclusion that the parasites were nourished at the expense of the beetle, the thread serving to convey the juices of its body to them.

‘It is very singular,’ he says, ‘to see living insects planted on the body of larger insects, from which they draw their subsistence by means of a thread or stalk.’ And then he goes on to compare these ‘vegetative Mites,’ as he calls them, with the ‘eggs’ of the Water Mites, which he found on Dytiscus and the Water Scorpion. The thread exists, and the Mites are attached by it to their host, but they do not draw nourishment through it from the beetle, for it is composed of their excrements.

The Myriapods are worm-shaped creatures, breathing by means of air-tubes, and furnished with a number of limbs closely resembling each other. There are two groups: the Centipedes and the Millepedes. The former have the body flattened, with one pair of appendages to each segment, the first pair being modified into piercing poison-organs, and they feed on living prey. The body of the Millepedes is round, with two pairs of appendages to each segment; they have no poison-organs, and their food consists chiefly, if not entirely, of vegetable matter.

There seems to be some doubt, however, as to whether Ju´lus, one of the commonest Millepedes, does not occasionally indulge in animal food. In Nature Notes (Jan. 1896) there was a review of the Cambridge Natural History (vol. v). The reviewer, in a brief summary of Mr. Sinclair’s part of the book (the Myriapods), said, after describing the Centipedes: ‘The millepedes, on the contrary, are sluggish vegetarians, with hard, cylindrical bodies, &c.’ On this a correspondent wrote in the March number: ‘Some time ago my attention was attracted to a large earthworm, writhing and twisting about on the garden path, as though in pain, or through having received some injury. On examining it more closely to ascertain the cause of its unusual movements, I found that a millepede had fastened itself to the side of the worm, and appeared to be boring or eating its way into the body, whilst the most violent efforts on the part of the worm were ineffectual in shaking off its antagonist. If the millepede is a vegetarian, what could be its object in attacking so harmless and defenceless a creature as the earthworm? The above, which I take to be a millepede, is the black or dark-coloured creature “with hard, cylindrical body” ordinarily found coiled up in a spiral under stones or rubbish.’

The editor, as a matter of course, referred the matter to the writer of the review. His reply was as follows: ‘If there is no mistake about the identity of the aggressor in the account cited above, the observation is one of considerable interest; for, so far as we are aware, it is the only case on record of a millepede being guilty of such conduct. But were it not for the positive statement that the species was the dark-coloured creature with a hard, cylindrical body, which is ordinarily found coiled up in a spiral under stones or rubbish—a description which exactly applies to the millepedes of the genus Julus—we should have concluded without hesitation that the struggle in question was merely one of those that habitually takes place between the centipedes of the genera Litho´bius or Geoph´ilus and the earthworms upon which they feed.’

Both the Centipedes and Millepedes are shy, light-shunning animals, and if we turn over some stones in the garden or in a walk through the fields we shall probably find specimens enough to serve us in getting some idea of both groups.

The Centipedes are sometimes called ‘Hundred-legs,’ but this implies the possession of many more legs than the creatures really have. In Norfolk and Suffolk the people call them ‘Forty-legs,’ and this is much nearer the mark.

Litho´bius forfica´tus, about an inch long and rufous brown in colour, is extremely abundant under stones and the bark of trees, and in cellars and outhouses. These animals run with great rapidity when disturbed, so that one needs to be on the alert to seize them when they are driven from the places in which they lurk. The body has nine principal and six subsidiary or smaller rings, and there are fifteen pairs of walking legs, besides the first pair, which are modified to serve as poison-organs. De Geer says that he never dared to pick up these Centipedes with ungloved hands, because he had seen a fly, which had been bitten by one, die on the spot, ‘which seems to be a sign that their bite is venomous.’ He examined their modified legs with a good microscope, but could not distinguish any opening. There is, however, an opening, as De Geer suspected, though he could not distinguish it; it lies near the point, and we may also trace the canal through the claw down to the poison-glands which lie, one on each side, at the base of the claws. The mouth parts resemble those of insects, and may be dissected out in the same way. When this Centipede walks, says De Geer, it does not use the last four pairs of legs, but drags them after it; but when it walks backwards, which it does as well as forwards, it then makes use of these four pairs of legs in the same way as the others. If we keep Lithobius alive we shall see that it can walk backwards, though it can scarcely be said to go as well one way as the other. From the same old writer some useful hints as to the method of keeping these animals may be gathered. Those that he kept in a vessel without any moisture soon died, and were quite dried up in twenty-four hours, which will teach us to keep them in a vessel with damp earth, shaded from light and heat.

Dr. Sharp[39] gives some interesting details about the breeding habits of Lithobius, and describes, for the first time, the uses of the two hooks on the under surface of the body of the female.

He experimented with Centipedes and Millepedes. Keeping them in large shallow glass vessels, the bottom of which was covered with a layer of earth, he fed the specimens of Lithobius on insects and worms, and sometimes on raw chopped meat, but they did not thrive on this as they did on prey which they could kill for themselves.