with claws; it seems clear that the bristles of the Annelidans, and the base within which they are retractile, are really legs, and lead the way to the jointed ones of the Condylopes.

I have before noticed the conversion of legs into oral organs, or their use as auxiliaries to them in the case of the Myriapods. Mr. Savigny, in his description of an animal, which seems the analogue of the electric centipede, observes that its four anterior legs are converted into tentacular cirri, affording an addional argument for the ancient opinion that the marine Myriapods, as they might be denominated, have some affinity with the terrestrial, since at least, in this instance, the same number of legs, are used as auxiliaries to the mouth.

The great majority of the Annelidans inhabit the water, and the tufts of bristles, sometimes forming fans, issuing in many cases from a dorsal and ventral conical protuberance, denominated by Savigny oars, and occasionally expanding so as somewhat to resemble them, seem in some degree analogous to the branching legs of the Branchiopod and Lernean Entomostracans, and are probably natatory as well as ambulatory organs, and means by which their Creator has fitted the locomotive ones to make their way through the matted sea-weeds and the mud when creeping after their prey, as well as to row through the water like a stately bireme. These oary feet, emulating in number those of the terrestrial Myriapods, and forming moreover, as was before stated, both a dorsal and ventral series, must enable them to move with considerable rapidity: those indeed that have observed their proceedings, describe them as both swimming and running with admirable ease and speed."

There is a Class of vertebrated animals, the Ophidians or serpents, which exhibit considerable analogy to many of the Annelidans, not only by their form and undulating movements, but also by the organs which effect their progressive motions, not indeed by means of bristles, but of parts that, pushing against the plane of position, propel the animal in any direction according to its will.

But the way in which this is effected having been clearly and most ably explained by an eminent and learned physiologist,' I need not here enlarge upon it but only observe that

1 Ibid. FIG. 2. c. c.

3 Lycoris agyptia PLATE VIII. FIG. 4.

4 Geophilus electricus.

2 See above, p. 224.

5 PLATE IX. FIG. 3.

6 See Otho Fabricius Paun. Groenland. 289, 298, &c. 7 Dr. Roget.

the motion of one tribe of the Myriapods, though produced by legs, exactly imitates that of the Ophidians, though produced by ribs; and very amusing it is to see the propogation of it from one extremity to the other in the Millipedes, like wave succeeding wave in the water: a still more striking analogy, as has been already remarked,' is exhibited by the larger centipedes, which seem almost models of the skeleton of a serpent. Serpents thus can move not only horizontally, but also up the trunks of trees, probably in a spiral direction, and some are said to have the power of darting from one tree to another. As these animals are not annulated, like the Annelidans, and cannot originate and continue motion by the alternate contraction and extension of the rings or segments of their body, which the nature of their integuments, their vertebral column, and muscular fibre, probably preclude, the wisdom of their Creator has subjected their ribs to their will, so that they can use them as motive organs.

Natatory Organs. The spurious bristle-armed legs of the Annelidans, especially those of Peripatus, have as it were led us to the mighty host of animals furnished with articulated, lolocomotive, or prehensory organs, or real legs and arms, varying in number-but as these will best finish the subject, I shall first consider those external instruments of motion which are peculiar to animals inhabiting the water, or moving through the air, beginning with the first, or those distinguished by natatory organs. I have already mentioned some of this description, as the oars of the paper nautilus and Annelidans,* and also the sails expanded by the former animal and several Molluscans. Before I consider the organs in question, where they are most conspicuous, in the fishes, I must give some account of those to be met with amongst the invertebrated animals, particularly the Condylopes. Several of the Cephalopods and Pteropods, and other Molluscans, have natatory appendages: in the former, as to many species, looking like little wings, often nearly round, attached to the lower part of the mantle that envelopes them; and, in the latter, assuming the shape and station of the dorsal and other fins of fishes, though totally different in their structure, not being divided into jointed rays, as in the animals just named.

1 See above, p. 225. 3 See above, p. 167. 5 See above, p. 142.

7 PLATE V. Figs. 6, 7, 8.

2 PLATE VIII. FIG. 1, 2,

4

See above, p. 258.

6 PLATE VII. FIG. 1.

Having mentioned these, I shall next advert more fully to the organs by which the great Sub-kingdom of animals with articulated legs move in the waters, whether they always inhabit them, or occasionally visit them. They may be divided into three distinct kinds. 1. Jointed legs, dilated towards their extremities, as in the common whirl-wig,' the little beetle that forms circles in the water, and in the tribe of crabs termed swimmers these I would call Pediremes. 2. Jointed legs, that terminate in a fasciculus of setiform branches, and are also connected with the respiration of the animal, these might be denominated Branchiremes, and are found in the Branchiopod Entomostracans.3 3. Those in which the inner side of the jointed leg has a dense fringe of hairs, called by Linné, by way of eminence, pedes natatorii, such as are found in many diving and other aquatic beetles-these might be named Setiremes. As the spurious legs to which the eggs are attached, observable on the underside of the abdomen of the female lobster, crayfish, and other long-tailed Crustaceans, are used also as natatory organs, they are ciliated for that purpose, and belong to this tribe. The same observation will also apply both to maxillary legs, and other legs of several animals of that Class. The velocity with which the diving-beetles move in the water by the action of these legs, and their suspension of themselves at the surface, by extending them so as to form a right angle with the body, when they come up for air, and the weather is fine and the water clear, affords a very interesting spectacle.

Amongst natatory organs, I must not overlook the tails of the long-tailed Decapod and several other Crustaceans, which terminate in a powerful natatory organ, consisting usually of five plates, densely ciliated at their apex, the intermediate one formed of the last segment of the abdomen, and the lateral ones articulating with a common footstalk giving them separate motion, the outer consisting sometimes of two articulations, as in the common lobster, and sometimes of only one, as in the thorny lobster; the intermediate plate, as in Galathea, sometimes consists of two lobes; these laminæ,when expanded, form a most powerful natatory organ, which, if we consider the weight of their body, must be necessary to keep them from sinking, and, by its vertical motion, to enable them to rise or sink in the water. But natatory organs are not confined to those of the trunk and abdomen, even those of the head sometimes assist in this kind of motion. Thus, in Cypris, an Ento

1 Gyrinus.

3 PLATE IX. FIG. 4. c.

2 Nageurs. Lam,

4 Dyticus.

mostracan genus, resembling a muscle, the mandibles and first pair of maxille have branchial appendages used also in swimming, and their antennæ are likewise terminated by a fasciculus of threads, which, according to Jurine, the animal developes, more or less, as it wants to move faster or slower.1 But the most important natatory organs are those which enable the vertebrated inhabitants of the waters, from the giant whale to the pigmy minnow, to make their way through the waves; it will be interesting to trace the analogies of the fins of these animals to the locomotive organs, whether wings or legs of other animals, especially Mammalians. Some we shall find sui generis, and calculated particularly for the circumstances in which the Creator has placed the great class of fishes and the rest of the marine animals; and others, in the course of our analysis, we shall observe gradually assuming the character and uses of an arm or leg.

The fins of fishes are membranes, usually supported by osseous or cartilaginous rays, which can open or shut, more or less, like a fan, but in some instances they consist of membrane without rays, and in others of rays without membrane. The rays are usually divided into two kinds; those which consist of a single joint, usually less flexible and pointed, whence they are called spiny rays, and those which consist of numerous smalt articulations, generally branching at their extremity, which are called jointed rays, these jointed rays may be regarded as precursors of the phalanxes of fingers and toes in the hands and feet of the terrestrial vertebrated animals. The first pair of fins, which are seldom wanting, and answer to the forelegs or arms of those animals, are called pectoral, and are usually placed on the side behind the gill-covers. The second pair, supposed to be analogous to the hind-leg, are called ventral, and are placed under the abdomen. Besides these, there is often a fin along the back, sometimes subdivided, named the dorsal fin; another under the tail, called the anal, and the tail itself terminates in a fin, one of the most powerful of all, which is named the caudal, and in some respects may also claim to be regarded as the analogue of the legs.

The, so called, fins of Cetaceans, are not properly fins, but legs adapted to their element as marine animals, the anterior pair having all the bones proper to those of mammiferous animals, covered with a thick skin, and wearing the appearance of a fin. In the sea-cow there are rudiments of nails in their pectoral fins, and they use them, both for crawling on shore,

1 Latr. Cours D'Entomologie, i, 430.

and for carrying their young, on which account they are called Manatins, of which Lamantins, their French name, is probably a corruption. The tail also of the Cetaceans, which is in the shape of the caudle fin of fishes, and somewhat forked, but placed horizontally, contains some bones, which appear like rudiments of those of legs, thus, for their better motion in an element they never leave, covered by their Creator with a tendinous skin, and enabling them by an up and down motion to sink to a prodigious depth, or to rise from the bottom to the surface of the ocean.

If we go from the Cetaceans to the Amphibians, we see a further metamorphosis of the organs of motion. The pectoral fins of the former are now become arms, with phalanxes of fingers, claw-armed, but still connected by skin for natatory purposes, and their caudle fin is converted into rudimental legs, with a very short intervening tail, and these legs are still of most use in the water. These circumstances induce some suspicion, especially, when we consider that the caudal fin of fishes is their most powerful locomotive organ, that it is the real annalogue of the hind-legs of the terrestrial mammalians.

3

The ventral fins sometimes seem to change place with the pectoral ones. This is the case with the fishing-frog tribe, in which the former are nearest to the head, and seem analogous to a pentadactyle hand, while the pectoral ones resemble a leg and foot, and the creature looks like a four-footed reptile. The Rays, in a system, are placed at a wide distance from these and yet they possess several characters in common, particularly in having the hinder part of the body antenuated into a tail more or less slender, and the enormous mouth or gullet of others are armed, as in the sharks, with a tremendous apparatus of teeth. Cuvier observes of one of them," that it can creep on the earth by means of its fins, like small quadrupeds, and that their pectorals discharge the function of hind-legs :$ so that there seems some ground for thinking that they are a branch diverging from the Selacians towards the Reptiles.

Fins, and their analogues, were given to aquatic animals, it should seem, solely for locomotion; and could we witness the motions of their different tribes, each in its place, and observe the play of these appendages, we should find them all so located in the body of the fish, and so nicely measured with