Now the microscope, or a powerful lens, will reveal the cause of this difference ; the threads of the cables and radii are perfectly simple, while the spiral threads are closely studded with minute globules of fluid, like drops of dew, which, from the elasticity of the thread, are easily separated from each other. * These are globules of viscid gum, as is easily proved by touching one or two with the finger, to which they will instantly adhere ; or by throwing a little fine dust over the nets, when the spirals will be found clogged with dirt, while the radii and cables remain unsoiled. It is these viscid threads alone that have the power of detaining the vagrant flies which accidentally touch the net.

The diversity in the secreting organs already alluded to, as well as in the spinnerets, is no doubt connected with this difference in the character of the silk ; and it is worthy of remark, that this diversity is greatest in such Spiders as the Epeirce, which spin geometric nets.

Immense is the number of globules of viscidity that stud the spiral circles of one of these nets. Mr. Blackwall, the able and learned historian of the tribe, has estimated that as many as 87,360 such pearly drops occurred in a net of average dimensions, and 120,000 in a large net of fourteen or sixteen inches diameter ; and yet a Spider will construct such a net, if uninterrupted, in less than three-quarters of an hour.

Scarcely less admirable are the ease and precision with which the little architect traverses her perpendicular or diagonal web of rope,— a skill which leaves that of the mariner who leaps from shroud to backstay in a ship's rigging immeasurably behind. To understand it, however, in some measure, look at this last joint of one of the feet

Mr. Richard Beck (" Trans. Micr. Soc," ix. 17) has ascertained that the spiral thread is, when first spun, of uniform thickness ; but, after some exposure, the viscid matter spontaneously accumulates at most regular distances, and forms itself into globules, which are larger and smaller alternately. It is a beautiful example of molecular attraction.

of our well-used Clubiona. is a cylindrical rod, ending in a rounded point ; every part of its surface is studded with stiff, rather long, horny bristles, which, springing from the side, arch inward towards the point. Now this array of spines effectually prevents a false step, for if any part of the leg, which is sufficiently long, only strike the thread, the latter is certain to slip in between the bristles, and thus to catch the leg. But more precision than this is requisite ; especially when we observe with what delicacy of touch the hinder feet are often used to guide the thread as it issues from the spinnerets ; and particularly with what lightning-like rapidity the larger net-weavers will, with the assistance of these feet, roll a dense webof silk around the body of a helpless fly, swathing it up, like an Egyptian mummy, in many folds of cloth, in an instant.

Look, then, at the extreme tip of the ultimate joint. Two stout hooked claws of dark horny texture are seen proceeding from it side by side, and a third of smaller size, and more delicate in appearance, is placed between them and on a lower level. The former have their under

CLAWS OF SPIDER.

or concave surface set with teeth (eighteen on each ii* this example), very regularly cut, like those of a comb, which are minute an the commencement of the series near the base of the claw, and gradually increase in length to the tip. These are doubtless sensible organs of touch, feeling and catching the thread ; and they, moreover, act as combs, cleansing their limbs, and probably

their webs, from the particles of dust and other extraneous matter which are continually cleaving to them.

There are Spiders in the sea also. I can show you one which is sufficiently common on the southern shores, sprawling and crawling sluggishly among the filamentous sea-weeds and branching flexible zoophytes. Here it is, Nymphon by name.

Its most prominent characteristic is the exceeding slenderness of all its parts, but especially its eight legs, which are greatly lengthened, each comprising eight joints, and no thicker than the finest thread. On the other hand, the body is reduced to a minimum ; the abdomen, which in the Spiders and Harvestmen of the land is so bulky as to constitute the chief volume of the animal, is here so minute that you will have some difficulty in finding it at all ; it is, in fact, that tiny atom of a point that projects between the hindmost pair of limbs. The thorax, indeed, is a little more developed ; but even this has scarcely any appreciable breadth or thickness, being little more than the extended line formed by the successive points of origin of the limbs.

The head, however, is distinct and well furnished. It is crowned with a short column, much as in the Harvestman, on the summit of which are placed four black eyes, set in square ; these, under the magnifying power which we are applying to them, gleam like diamonds, the light being highly refracted through them. It is the high refractive power of these eyes, as of those which we have lately been examining, which makes them appear black ; for, as I have explained, they are really transparent lenses, covered with polished cornea?, and furnished with the other essentials requisite for the transmission of the rays of light to the optic nerve, or, as in this case, direct to the brain.

In front, you see, the head projects into a stout oval or cylindrical proboscis, terminating in a small mouth and stout jaws, and furnished at the sides with a pair of spinelike palpi, and a pair of pincer-claws (modified antennae) somewhat resembling the nippers of a Crab or Lobster.

Such is the outward form of this tiny speck, the whole body of which scarcely equals in dimensions a quarter of an inch of sewing cotton. And now I will beg your attention to the singular manner in which digestion is carried on in this atom. You will discern it plainly enough through the brown, but translucent skin. If you look carefully at either of the long, many-jointed legs, you will see that it is permeated by a central vessel, the walls of which contract periodically with a pulsation closely resembling that of a heart, by which granules or pellucid corpuscles, floating in a clear fluid, are forced forward. There is no uniformity in the direction of the pulsatory waves ; sometimes, as in the limb we are watching, they proceed from the body towards the extremity ; but, in some of the others, we shall probably find, even at the same moment, that the waves have an opposite course ; and this contrariety may occur in two contiguous limbs on the same side of the animal. By continuing our observation for some minutes, we shall find also that its force is varying and uncertain ; strong and regular at one time, weak and irregular at another, and sometimes even quite intermitted, or, at least, quite imperceptible.

By selecting a limb in which the movements are strong, you may trace the vessel to its termination in a blind sac in the last joint but one of the limb ; and then follow it up to its junction with a great vessel which runs longitudinally through the trunk, of which all the vessels that permeate the limbs are branches, and whence the circulating globules all proceed. This great vessel is the stomach; and this circulation is the provision for dispersing the nutritive properties of the food to all parts of the system. There is, in these humble and simplyorganised animals, no proper blood ; or, at least, none included in a system of arteries and veins ; but the products of digestion are carried to the most distant parts of the body through this extraordinary development of the' stomach or intestine (both in one), and through this series of blind canals, by means of their own irregular contractions, aided by the muscular movements of the body and limbs.

You would scarcely forgive me if I took do opportunity of showing you the Cheese-mite, that first object of wonderto every child that looks through a magnify ing-glass. And it could not be more suitably introduced than in connexion with its cousins, the Spiders and Harvestmen. Well, fortunately, we need not search far for specimens; for here, in the cavity of this almost defunct skeleton of a cheese, we can find as many millions as you can reasonably desire to select from. Here is a fat one; we will take him.

You can see with a pocket lens that it has a plump, polished, oval body, of a pellucid white hue, and eight short red legs ; but for more than this we must go to the tube. Look at him now, as he lies on his back,, helplessly sprawling and throwing his feeble legs about, in the live-box.

His oval body is divided by a transverse furrow into thorax and abdomen, like a Beetle's; and there is another division between the head and thorax, wherein it differs from the Spider's. The first two pairs of legs are separated by an interval from the last two pairs ; they are all of a translucent pale red hue, as is also the head : each consists of seven short joints, the last of which has a sort of heart-shaped pad, something like a horse's hoof, and a single hooked claw, which works against its sole.

The structure of the head cannot be seen satisfactorily otherwise than by crushing the Mite in the compressorium;. a process which, when we remember how many thousands we crush down in our oral compressorium every time we eat ripe cheese, needs not excite much compunction. We must put a drop of water between the plates, in order to wash away the opaque granules which will escape from the bodies of the animals; after which the skin, and all the solid parts, will be left beautifully clear and distinct. Moreover, by putting half a dozen specimens in at once, we shall secure them pressed in various aspects, and be pretty sure of some perfectly flat and symmetrical.

I have one under such conditions ; the parts of the mouth nicely expanded, and the whole well displayed. Xoav for a high power ; for, to discern this properly, we cannot do with less than 600 diameters.

HEAD OF CHEESE-MITE.

Viewed from beneath, we see a broad labium, nearly square, divided at the tip into two blunt points, with a sharp notch between them. The two lateral edges are, as it were, buttressed by the pair of palpi, which are thick, and consist of four joints each ; these are distinguished by the bristles at each joint, though the whole are united or soldered, as it were, to the sides of the lip.

The upper portion of the mouth is formed by two stout mandibles, which are jointed to the front of the head, and can be either widely expanded, or brought together, so

as to form a covering to the labium. They are pincerform, like the claws of a crab, the two fingers being strongly toothed on their opposing surfaces. They thus form effective prehensile instruments. These mandibles can be advanced separately or together, and the whole head can be elevated or depressed.

In the water of ponds we may frequently see, playing among the sub-aquatic vegetation, bright-coloured Mites ; sometimes rich velvety green, sometimes purple, but more commonly brilliant scarlet; often curiously marked with sinuous patterns or spots of black. They swim freely and evenly, by means of rapid rowings with their legs, which are thickly fringed with long hairs. I have one here, which seems to be the Hydrachna histrionica. It is a little, flat, circular, cushion- or cake-like creature, scarlet, with four clouds of black on its back, and about one-sixth of an inch in diameter. You may notice the effective oars which the legs form, by means of their thick fringe of hair ; and, in particular, the power which the hind pair possess, by reason of the enormously dilated hip-joint, affording space for broad and powerful muscles.

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