another form of the same class of animals. Meanwhile, I will just point out a beautiful though minute proof of design in a point of the structure of the cells connected with these pearly chambers. If you look closely, you will see that the spines of the margin are not found on those cells that carry the pearls ; and moreover, that they are also wanting on the approximate edges of the two cells that lie behind every such pearl-bearing cell. Now the reason of this omission is obvious. The spines projecting obliquely would interfere with the gaping of the door ; and hence they are invariably absent there.

I happen to have in my aquarium a living individual of another species belonging to the same class, and agreeing with this in all essential particulars of structure, though widely different in form. The difference, however, is mainly dependent on a rather unimportant point of arrangement ; for the cells, instead of being set side by side and end to end, in quincunx fashion, to an indefinite extent, on two surfaces of a plane, are disposed on one single surface, and in longitudinal rows of two or three cells abreast ; thus narrow ribbon-like branches are formed, which now and then divide into two, then these into two more, and so on. These branches thus become fan-shaped, which, by being slightly curved, became segments of funnels ; and the peculiar elegance of this coralline consists in the mode in which these branches are set on the stem, viz., in an ascending spiral curve, so that the effect is that of several imperfect funnels set one within another, but which yet you perceive, by turning the whole gradually round, to compose a single corkscrew band of successive fans. This whole structure stands upright in its natural state, like a little compact shrub growing from a root ; and as a good many are commonly associated together, they form a sort of mimic grove, fringing the sides of dark rocky sea-pools.

The species is called the Corkscrew Coralline, or sometimes, the Bird's-head Coralline, the latter name being assigned to it for a reason which you will presently perceive. The appellation by which it is known to naturalists is Bugula avicularia.

We drop our specimen into a very narrow cell, composed of parallel walls of thin glass, a very minute flattened tank, in fact, such as can be put on the stage of the microscope. Here, bathed in its native sea-water, as clear as crystal, we shall see it opening and expanding its numerous polypides with the utmost activity and evident enjoyment.

You gaze ; but you know not what you see. The presence of many lines, representing transparent vessels of strange and dissimilar shapes, overlying each other ; and the swaying to and fro of curious objects, which strike now and then forcibly across the field of view, are quite bewildering. I must act the showman and tell you what to see.

The cells are oblong, shaped much like a sack of corn, with a spine ascending from each of the upper corners. Each stands on the summit of its predecessor in the same row, and side by side with those of its fellow-rows, in such an order that the top of one cell comes opposite the middle of the one beside it. The top of the sack is rounded, and appears closed, but we shall presently find an opening there. The broad side that faces inwardly has a large elliptical transparent space occupying nearly its whole surface; this is covered with a very thin and elastic membrane, and answers a peculiar end. Just below one of the spines that crowns the summit of the cell on one of the edges, is situated a little lump, to which is attached, by a very free joint, an object which you will perceive to bear a remarkable resemblance to the head of a bird of prey. It has a beak strongly hooked, with two well-formed mandibles, of which the lower is movable, shutting into the cavity of the upper ; you observe it deliberately opening, like that of a bird, only stretching to an enormous width of gape, and then closing with a strong and sudden snap. Now and then the whole head sways backward and forward on its joints; and these movements, combined with the fitful and apparently spiteful snappings, performed by many birds' heads scattered about the branch, are highly curious and amusing.

The birds' heads, however, are not the living inhabitants of the cells ; they are not integral parts of them. The cells have their proper inhabitants, each dwelling in its own ; and each essentially formed on the same plan as the "baby with the tucked-up knees," that makes the Sea- mat for his cradle-house.

In order to get a good view of the tenant here, you must move the stage about till you find that the branch is presented to your eye sidewise. Directing your attention then to the lateral edge of a single inhabited cell, its summit is seen to protrude diagonally, towards the inner side (i.e., towards the axis of the spire), a tubular mouth which is membranous and contractile. When the animal wishes to emerge, this tubular orifice is pushed out by unfolding the integument, and the tentacles are exposed to view, closely pressed into a parallel bundle; the unfolding of the integument, that is attached at their base, goes on till the whole is straightened ; when the tentacles diverge and assume the form of a funnel, or rather that of a wide-mouthed bell, the tips being slightly turned out. They are furnished with a double row of short cilia in the usual order, one set working upward, the other downward. Their base surrounds a muscular thick ring, the entrance to a funnel-shaped sac, the substance of which is granular, and evidently muscular, for its contractions and expansions are very vigorous, and yet delicate. Into this first stomach passes, with a sort of gulp, any animalcule whirled to the bottom of the funnel by the ciliary vortex ; and from thence it is delivered, through a contracted, but still F rather wide gullet, into an oblong stomach, the lower portion of which is obtuse. An extremely attenuated duct connects this, which is probably the true stomach, with a globular, rather small, intestine, which is again connected by a lengthened thread with the base of the cell. By an arrangement common to the ascidian* type of the digestive function, the food is returned from the intestine into the true stomach, whence the useless parts are discharged through a wide and thick tube that issues from it close behind the point where the gullet enters. This tube passes upwards parallel to the gullet, and terminates by an orifice outside and behind the base of the tentacles. All these viscera are beautifully distinct and easily identified, owing to the perfect transparency of the walls of the cell, the simplicity of the parts, and their density and dark yellow colour. All of them are manifestly granular in texture, except the slender corrugated tube which connects the stomach with the globose intestine : this is thin and membranous, and is doubtless, if I may judge from analogy, capable of wide expansion for the passage of the food-pellet.

The sudden contraction of the polypide into its cell upon disturbance or alarm, and its slow and gradual emergence again, afford excellent opportunities for studying the forms, proportions, and relative positions of the internal organs. In contraction, the globular intestine remains nearly where it was; but the stomach slides down into the cell behind it, as far as the flexible duct will allow, and the thick gullet bows out in front, showing more clearly the separation between it and the rectum, and the insertion of both into the stomach. This retraction is, in part, effected by a pair of longitudinal muscular bands, which are inserted at the back of the bottom-part of the cell, and into the skin of the neck below the ten- * The Ascidia are a low order of animals growing in masses in the sea, with bodies like little leathern pouches : whence their name, from a Greek word clctkoq (askos), meaning pouch.

tacles. The contraction of these bands draws in the integument, like the drawing of a stocking within itself, and forces down the viscera into the cavity of the cell, which is probably filled with the vital juices.

Besides the hind bands, there is one, or a pair of similar muscular bands attached on each side of the front part of the base of the cell, and inserted similarly into the neck. By watching the contraction of these, you will be enabled to determine the use of the membrane-covered aperture up the front of the cell. At the moment of the retraction of the viscera into the cell, a large angular membrane is forced outward from the front side, which is protruded more or less in proportion to the degree of withdrawal of the polypide ; and as the latter emerges again, the membrane falls back to its place. It is evident, then, that this is a provision for enlarging the cavity ; the walls are horny, and probably almost inelastic; but when the stomach forces the intestine forward, and the thick gullet is bent outward by the withdrawal of the neck and tentacles, the needful room is provided by the bulging out of this elastic membrane, which recovers its place by the pressure of the surrounding water, when the pressure of the fluids within is removed.

Now, after watching these movements of the polypides, and the various structures whose forms and limits those movements reveal, it will become manifest to you that there is no visible organic connexion between the animal, distinctively so called, and the curious bird's head. This latter has a muscular system of its own, by means of which its energetic motions are performed; but it appears quite isolated on the outside of the calcareous cell, and wholly cut off from the interior by the knob on which it works, and by the thickness of the cell-wall. Both knob and wall appear quite imperforate ; and yet we cannot but presume that some connexion exists, perhaps through the medium of an exceedingly delicate and subtile, but f 2 living tissue, which may be presumed not only to line, but also to cover the strong cell; just as the strongenvelope and spines of a Sea-urchin are covered with a thin film of living flesh.

The functions and use of these singular processes are as obscure as their connexions with the animal. Yet, that they play some important part, we may almost certainly infer, from the general prevalence of similar or analogous appendages among the various forms of this class. The globular pearls which you lately saw on the Sea-mat are but another form of bird's head ; and the falling-door answers to the opening and shutting mandible. The forms, indeed, of these organs are very diverse, and sometimes they are greatly disguised. But what about their function 1 More than one observer has noticed the seizure of small roving animals by these pincer-like beaks; and hence the conclusion is pretty general, that they are in some way connected with the procuring of food. But it seems to have been forgotten, not only that these organs have no power of passing the prey thus seized to the mouth, but also that this latter is situated at the bottom of a funnel of ciliated tentacles, and is calculated to receive only such minute prey as is drawn within the ciliary vortex. I have ventured to suggest a new explanation. The seizure of a passing animal, and the holding of it in a tenacious grasp until it dies, may be a means of attracting the proper prey to the vicinity of the mouth. The presence of decomposing animal substance in water invariably attracts crowds of infusory animalcules, which then breed with amazing rapidity, so as to form a cloud of living atoms around the decaying body, quite visible in the aggregate to the unassisted eye; and these remain in the vicinity, playing round and round until the organic matter is quite consumed. Now a tiny worm or other animal caught by the bird's head of a Polyzoon,* and tightly held 7

Page 11 of 66