book to the classes it is intended for. The arrangement is well enough; and when the deficiencies are filled up by experimental illustrations, or verbal descriptions, we dare say that it will answer the purpose of enabling the student to draw up, at his leisure, more copious notes and perspicuous illustrations than those with which Dr. Fyfe has supplied him.

On the Structure and Habits of the Seal. By John Harwood, M.D., F. L.S., Professor of Natural History in the Royal Institution.

[This communication contains the outline of a discourse on the above subject, delivered to the members of the Royal Institution, by Dr. Harwood, on Friday evening, the 16th of February, 1827. It was illustrated by numerous specimens of skeletons, and of stuffed animals from the Museum of the Royal Institution, and from the valuable collection of Mr. Brookes.]

I HAVE principally been induced by two motives to select the Seal as the subject of the present discourse: the one is, that it has not attracted that general and popular notice with which its habits and peculiarities deserve to be viewed; and the other, that throughout the whole extent of animal life we discern no more beautiful and obvious adaptation in structure to those peculiarities and habits than are presented to us in the anatomy of this creature; indeed, these striking appropriations are so numerous, that it becomes difficult to make choice of those most worthy of attention. Externally, the seal is of an elongated form, its neck powerfully muscular and long, and its body formed like that of a fish, broadest across the chest, and gradually tapering to its hinder extremities. For the convenience of swimming, its fore limbs are so short, as to appear destitute of some of the bones and parts found in those of land-quadrupeds: for we only see externally the feet, having their toes provided with sharp claws; but they are so enveloped in broad membranes as not to be readily traced, though capable of free motion. Such a capability, however, only applies to our northern seals, and a few other species; for the eared kinds of the South Seas have their toes almost immovable, and furnished with flat nails on the fore feet. After the gradual tapering of the body, which terminates in a short flattened tail, the hinder

feet are observed to be furnished with still broader membranes, which in many South Sea species are even extended beyond the ends of the claws, whereby the extent of surface is greatly increased; but in all, aided by the powerful muscles of the spine, these feet act with immense force on the surrounding fluid, and produce an extremely rapid progression. From such external characters, a beautiful connexion is at once observed between the seal and those aquatic animals which surround it, its feet, for example, being intermediate in their structure between the simply webbed ones of the otter and beaver, and the flattened fin-like ones of the manati, the whales, and other cetacious mammalia which are more exclusively adapted to a watery element. But in the skeleton of the seal, these gradations and adaptations are still more apparent: though composed of the usual number of bones, the length and flexibility of its neck is of the highest importance in its economy; for, by the slightest inclination of the head, at the end of this long lever, in any direction, while diving, its centre of gravity becomes instantly changed at its will; and thus are its submarine chases, even after the swift salmon, rendered so marvellously successful, that its only mode of escape consists in darting into the shallows. In the general form of the skeleton, seals bear no very distant relation to the weasels, the chest having an unusual extent of motion, by the free articulation of its vertebræ, and, as in those animals, the liver and lungs are each divided into several distinct lobes, that they may glide smoothly over each other, and not oppose the great curvature to which their bodies are liable. On the same principle, their ribs are placed farther asunder than in most others; while the lumbar regions and pelvis, as in all diving animals, are long and narrow, for the attachment of powerful muscles. We now see that the limbs, although so curiously shortened for aquatic operations, possess the same number and arrangement of bones as those of animals whose actions are terrestrial, subject, however, to interesting modifications; for instance, in the fore-feet, the thumb or inner toe is the strongest, and the outer the weakest; but in the hinder feet, to increase the force and extent of membranous surface opposed to the water, the two outer toes are far the longest and strongest.

From such an aquatic conformation, then, it is sufficiently obvious that the movements of the seal on the land are necessarily slow and imperfect: they have been, not unaptly, compared to those of a caterpillar, being chiefly effected by vertical flexures of the spine. Nevertheless, even under these disadvantages, seals defend themselves and their young with their teeth, with great courage and address; thus I recollect having seen a seaman who had been most severely wounded from too daringly attacking a large seal. It was observed by Aristotle, that most animals have their fore teeth sharp and their inward teeth broad; but that the seal has them all pointed; now, in fact, in the different species of seal, the skull not only affords much variety in its form, but their teeth differ so greatly from each other, that nothing would be more easy, were it by any means desirable, than to substitute new generic names for almost every known species. These differences are well exemplified in the various specimens before you, in which we observe their front teeth to vary in number, having either four or six above and four below, while their molares vary from sixteen to twentyfour, all of which, in common with their canine teeth, have more or less pointed surfaces.

In the Northern seals, the front teeth above have single points; but in the antarctic species, the four middle, upper, and, indeed, lower front teeth have a double edge, the two outer ones having single points their molares are either simply conical, like those of the common seal, or are each armed with three points as in the Phoca Grænlandica.

As sub-aquatic pursuits were those destined for the seal, and as these were liable to be often accompanied with labour and difficulty, it is obvious that they could not be carried on by animals internally organized like those of the land; for the necessity for so frequently rising to the surface to breathe, would have been an effectual impediment to their success. The Creator has, therefore, so modified the mode of circulation in the seal, that this inconvenience has been counteracted, and yet this has not been effected as in the reptiles; for in them the vessels of the heart are so constructed, that the blood can flow freely through them, without going to the lungs, and thereby occasioning a necessity for breathing; nor (which

would produce the same effect) do the auricles of the seal communicate, as was formerly thought. On the contrary, in the seal the original type in the construction of the heart is still retained, as also in the walrus and otter, and other aquatic mammalia, with this exception,-that the veins which return the blood to the heart are so much enlarged, that they are capable of changing their office, and becoming reservoirs for receiving and retaining the blood in its progress to the heart. Thus is the right side of the latter, and the lungs, prevented from being oppressed by its superabundance when the creature is under water, and incapable of breathing, and thus is its life sustained. The largest of these venous reservoirs exists in the liver of the seal; but its whole venous system, like that of the walrus and the whales, is very greatly developed. If I may be allowed the expression, like most other aquatic mammalia, the seal appears to be literally gorged with blood; its blood is moreover of an unusually dark colour, being almost black, which property it perhaps acquires by its constant liability to become arrested in its course; and hence, perhaps, the necessity for so much blood in its circulating system-yet the animal heat of the seal is very great.

We shall next briefly advert to some of the senses of this animal. Its very large and dark eyes being directed more forwards than in any other aquatic quadruped, added to the round and human appearance of its head, when raised above the surface of the water, doubtless caused it to contribute greatly towards the formation of those ideal marine monsters of which the ancients have favoured us with so many accounts. The eye of the seal is provided with a most perfect membrana nictitans, or winking membrane, the use of which it is rather difficult to conceive in aquatic animals, except to shield their delicate organs from the too powerful effects of the light, in rapidly rising from the depths to the surface. The pupil of the seal is vertical, like that of the cat; but its soft expressive physiognomy, which more nearly resembles that of the dog than any other quadruped, and is equally expressive of superior intelligence, is not affected by the cat-like form of the pupil, in consequence of the dark colour of the iris. But the greatest peculiarity in the construction of its eye, is a narrow zone, or

two zones, as in the Phoca monachus of the Grecian Islands, encircling the globe, of a thinner texture, so much so as to be only one-fourth part of the usual thickness, and more flexible than the rest of the sclerotic coat; and as the straight and oblique muscles of the globe are inserted anteriorly to these flexible zones into a thicker part of the tunic, it is probable that their simultaneous contraction may alter the length of the axis of the eye, and the form of the transparent cornea, by approaching the latter to the retina, and by rendering it more or less convex, and thus better adapt it to the different media in which the creature lives. I think this the more likely, because I have often observed that seals, on first appearing on the surface of the water, appear somewhat bewildered, and do not distinctly discern objects, till their eyes have had time to adapt themselves to the more rare medium to which they are exposed.

The nose of the seal is an organ of more perfect formation than that of any other quadruped. The nostrils are most accurately closed at the entrance by very perfect valves, to prevent the ingress of water when it dives, and, indeed, at all other times, except when it respires. Its breathing also, at all times, occurs at very irregular intervals, often extending to half a minute between each inspiration, but the quantity of air it then receives is very great. As to the internal formation of the nose, it possesses one of the most beautiful structures which the whole class exhibits, especially from the amazing number of the convolutions of those bones on which the infinite ramifications of the olfactory nerves are spread. It has, indeed, been computed by Sir Busic Harwood, that the smelling surface in the nose of a single seal amounts to the enormous extent of two hundred and forty square inches. Now it is no less worthy of remark that something of this curious complication in the organ of smelling likewise obtains in other aquatic animals, and especially the otter, which is a very remarkable circumstance, when we consider that, as before observed, their nostrils, like their ears, are most accurately closed by valves, to prevent the entrance of the water when they dive, and, indeed, at all other times, except during breathing. A question, therefore, naturally arises, that if, in the pursuit of their prey, or other sub