But, in order to obtain a more precise idea of the structure of this tiny creature, we must manage to restrain its liberty a little, by applying gentle pressure with the compressorium ; just sufficient to confine it without hurting it. The body is inclosed in a broad carapace, shaped much like a heraldic shield, but very convex on the back, and terminating behind in a slender point or spine, which is cut into minute teeth along the edges. Below this shield is seen the body, with three pairs of legs, a great proboscis in the middle pointing downwards and backwards, and the anal fork, which consists of a bulbous base and two diverging points^ which project behind under the spine of the shield.

The legs are exclusively swimming organs: they have no provision for grasping, no claws or hooks, nor do they appear to be capable of being used for crawling on the ground, or for climbing among the sea-weeds. They are fringed along one edge with long and stout, but somewhat flexible, spines, of which those that are nearest the trunk seem more rigid, and are directed more at right angles to the limb, than the rest. The legs are formed of many imperfect joints, and the second and third pairs are- -double from the basal joint outwards, while the first pair are simple. In the fore part of the body a large eye is placed, deep-seated, which is of a roundish form, and is intensely black both by reflected and transmitted light. On the summit of the forehead are placed a pair of thick flexible horn-like organs, which are abruptly bent in the middle, and which I believe represent the first pair of antenna?. This, then, is the first stage of the Barnacle— the form under which it appears when it is hatched from the egg.

YOUNG OF BAEXACLE.

Among the multitudes which have been evolved •during these last few days, and which are now swimming at large in the tank, we may be able to detect some that have passed through their first stage, and, having moulted their skin, have attained a more advanced form. Here is one, which by its superior size seems to have made some progress towards maturity.

Yes, here are more. These are evidently in their second stage. There is an increase in length ; for, whereas the

former was only —J-yth of an inch in length, these have attained to a length of T\jth of an inch. Yet this increase is observable in no other dimension than that of total length ; and this is due to the development of the terminal spine of the shield, which is now much produced, and cut into minute teeth. The anal fork is also attenuated, lengthened, and bent abruptly downward at the base, where it is very mobile; another bend in the middle throwing the extremity into the horizontal again. The delicately membranous pouch-like proboscis is more clearly seen beneath the breast, the extremity of which is directed backwards. In front of this organ there are two decurved very mobile bristles, set on pedicles, or stalks, the whole closely resembling the internal antennae in the higher Crustacea. The lateral horns or external antenna? appear to terminate in a very delicate brush of hairs, which does not seem to be capable of being protruded.

The little animals in this state swim, generally, back downward ; though they frequently assume a perpendicular position, both direct and reversed. I see them now occasionally resting on sea-weeds and Diatomacece, though the limbs seem even worse fitted than before for crawling, since the spines or bristles with which they are fringed are much increased in length, especially on the third pair.

A specimen nearly twice as large as these last affords us an opportunity of tracing the Barnacle to another point of its transformations. The modifications are chiefly in the proboscis and the anal fork. The former now points directly downwards ; is furnished with a pair of minute spines on its anterior side, and with a terminal hook ; while its posterior side is set with strong vibrating cilia. The anal fork is greatly increased in dimensions, has its edges armed with spines articulated to its surface, and is marked with longitudinal *&' lines which resemble corrugations. The under-surface of the body is also muck corrugated transversely.

In the first moult the spine of the shield was greatly increased, the size of the body itself remaining stationary; in the second moult the ratio is reversed, the body has largely increased, but the spine is nearly unchanged.

We cannot follow the metamorphosis any farther by personal observations ; but from the researches of others, and especially of Mr. Darwin, we know that other stages have to be passed before the final fixed condition is attained. As yet no perceptible advance has been made, by either of the two moultings which we have traced, from the free, jerking, dancing Water-flea that was first hatched, tow Tards the sessile Barnacle inclosed in its shelly cone of several valves, and firmly fixed to the solid rock ; and we are yet at a loss to imagine how such a change can be effected.

Nor is the matter apparently helped by the next moult; for, though there now ensues a great change of form, it does not seem to resemble the adult Barnacle much (if at all) more than before. If described without reference to its parentage, it would still be considered an Entomostracous* Crustacean, or Water-flea, but removed to another tribe. It represents, in fact, a Ci/pris/f the body with its fringed limbs being now included within two convex valves, like those of a mussel or other bivalve shell, either united by a hinge along the back, or rather soldered together there, so as only to allow a slight opening and closing, by the elasticity of their substance. The fore part of the head is now greatly enlarged, as are also the antenna', which project from the shell. The

From two Greek words—iprofior (entomos), cat up, and oarpaKov (ostrakon), a shell. A term applied to a group of the Crustacean* with minute bodies very much divided and inclosed in a shellv covering.

See figure on p. 181.

single eye is separated into two, which are large and attached to the outer arms of two bent processes placed within the body, in the form of the letters UU. The legs are increased by the addition of two pairs, and these are doubly bent in a zig-zag form, and can be protruded from between the valves.

It is a highly curious fact that the infant Barnacle has thus passed through two distinct types of animal life, those of the Cyclops and the Cypris. These are not one type in different stages, as might be reasonably presumed. The young of Daphnia and of Cyclops are so much alike, that it would be natural to presume the young of Cypris to be of the same form ; in which case, we should have in the young Barnacle merely the first and second stages of Cypris. But it is not so. Cypris does not pass through the Cyclops form at all ; for, according to Jurine, the young when hatched have the appearance of the perfect animal, though varying a little in the shape of their shells.

It is in this second form, which may be considered the pupa of the Barnacle, that the animal quits its free, roving life, and becomes a fixture for the remainder of its days. And this is a most wonderful process: so wonderful, that it would be utterly incredible, but that the researches of Mr. Darwin have proved it incontestably to be the means by which the wisdom of God has ordained that the little Water-flea should be transformed into a stony Acorn Barnacle.

Having selected a suitable place for fixing its re.-idence, such as those massive rocks which sustain the impetuous billows on our sea-worn coasts, the great projecting antenna? manifest a new and unprecedented function. Glands situated at their base secrete a tenacious <:lue, which, being poured out in great profusion, cements the whole front of the head to the rock, including and concealing the antennae themselves. The cement rapidly sets under water, and the animal is henceforth immovable.

It now moults its skin once more. Another great change takes place; the bivalve shell is thrown off, as are also the eyes with their bent supports, and it is seen to be a true Barnacle, though as yet of minute dimensions, and with its valves in a very rudimentary condition. It is now the representative of a third type among the Crustacean forms, for it is in effect a Stomapod;* such as the Opossum Shrimp (Jfysis), for example, with the shield composed of several pieces, stony in texture, on account of the great development of their calcareous element, and so modified in form as to make a low cone, the legs (become the cirri, or what I have above called the "fingers") made to perform their movements backwards instead of forwards, and the whole abdomen reduced to an almost invisible point.

Marvellous indeed are these facts. If such changes as these, or anything approaching to them, took place in the history of some familiar domestic animal,— if the horse, for instance, were invariably born under the form of a fish, passed through several modifications of this form, imitating the shape of the perch, then the pike, then the eel, by successive castings of its skin ; then by another shift appeared as a bird ; and then, glueing itself by its forehead to some stone, with its feet in the air, threw off its covering once mote, and became a foal, which then gradually grew into a horse;— or if some veracious traveller, some Livingstone or Earth, were to tell us that such processes were the invariable conditions under which some beast of burden, largely used in the centre of Africa, passed,—should we not think them very wonderful 1 Yet they would not be a whit more

From the Greek aro\ia (stoma'), mouth, and ttovc (pons), foot. A name given to those Crustaceans which have proper feet near the mouth.

wonderful, in this supposed case, than in the case of the Barnacle, in whose history they are constantly exhibited in millions of individuals, and have been for ages ; even in creatures so common that we cannot take a walk beneath our sea-cliffs, without treading on them by hundreds !

Chapter XIII. Spiders and Mites

Spiders, I am sure, are not favourites with you. With the exception of the poor prisoner in the Bastille, who had succeeded in taming a Spider,—the only creature besides himself that inhabited his dungeon,—I do not think I have ever heard of any one who loved or admired Spiders morally. Yet, physically, we may find much to admire in them, as net a few naturalists have done before us ; there are men who have devoted their lives to the study of this unamiable race, and who have discovered in them the same wondrous skill, and the same perfect adaptation of organ to function, of structure to habit, that mark all God's works, whether we think them pretty or ugly, amiable or repulsive.

I am going to show you some of these pieces of mechanism. Remember that the whole tribe is sent into the world to perforin one business: they are commissioned to keep down what would otherwise be a " plague of flies." They are fly-butchers by profession • and, just as our beef and mutton-butchers have their slaughter-house, their steel, their knives, their pole-axe, their hooks, so are these little slaughterers furnished with nets and traps, with caves, with fangs, and hooks, and poisonbags, ready for their constant work. They have, in fact, nothing else to do : their whole lives are spent in slaughtering,—with the exception of rearing fresh generations of slaughterers,—and I suppose they think, and are intended to think, of nothing else.

Page 31 of 66