confinement, change of air and temperature, and occasional exposure to light for some hours, as from mere starvation. It is well-known, for example, that, as a general rule, the Batrachia endure starvation most remarkably."

The gills of the Proteus are very apparent, and of a reddish colour, on account of the blood that circulates through them. I have often witnessed this phenomena by means of the ingenious arrangement invented by Dr. Beale, by which the creature was held firmly in its place while a stream of water was kept constantly flowing through the tube in which it was confined. The blood discs of this animal are of extraordinary size; so large, indeed, that they can be distinguished with a common pocket magnifier, even while passing through the vessels. Some of the blood corpuscules of the specimen described above are now in my possession, and, together with those of the lepidosiren, form a singular contrast to the blood corpuscules of man, the former exceeding the latter in dimensions as an ostrich egg exceeds that of a pigeon.

The colour of the Proteus is pale faded flesh tint, with a wash of grey. The eyes are quite useless, and are hidden beneath the skin, those organs being needless in the dark recesses where the Proteus lives. Its length is about a foot. What are the natural habits of this strange animal, what is its food, of what nature is its development, and what is its use, are a series of problems at present unanswered. By some writers it has been thought to be merely the larval state of some large Batrachian at present unknown; but the anatomical investigations that have been made into its structure seem to confirm the idea that it is a perfect being, and one of those species which carry the gills throughout their whole existence.

IN the NECTURUS, the head is much broader and flatter and the tail shorter than in the preceding species. This animal belongs to the same family as the proteus, but is a native of America, being found in the Mississippi and several of the lakes. It is rather a large animal, attaining, when adult, a length of two or three feet, and being of a thick and sturdy make. The gills of this creature are large and well tufted, and the limbs are furnished with four toes on each foot, but without claws.

The general colour of this creature is olive-brown above, dotted with black, and with a black streak from the nostril through the eye, and along each side to the tail. Below it is blackish brown with olive spots.

OUR last example of the Batrachians is the curious SIREN, or MUD-EEL, as it is sometimes called, on account of its elongated eel-like form and its mud-loving habits.

It is a native of several parts of America, and is found most plentifully in Carolina, where it haunts the low-lying and marshy situations. The rice-grounds seem to be its most favoured localities, the muddy soil being the substance best adapted for its means of

progression. Its food seems to consist almost entirely of worms and various insects, of which it will consume a considerable quantity every day. A fine specimen that lived for some time in the Zoological Gardens used to feed upon earthworms, of which it would devour about eighteen or twenty every two days. This individual passed the greater part of its time beneath the thick stratum of soft mud with which the bed of the basin was profusely covered. This was a very long specimen, and by an uninitiated observer would probably have been taken for an eel.

The head of the Siren is small in proportion to the size of the animal, the eye is very small, and the gill tufts are three in number on each side, and beautifully plumed. It has only one pair of legs, the hinder set being wanting, and the front pair are extremely small, and of no practical use in progression. It has only three toes on each foot. The colour is dark blackish brown, and the length of a fine specimen is about three feet.

FISHES.

IN the FISHES, the last class of vertebrated animals, the chief and most obvious distinction lies in their adaptation to a sub-aqueous existence, and their unfitness for life upon dry land.

There are many vertebrate animals which pass the whole of their lives in the water, and would die if transferred to the land, such as the whales and the whole of the cetacean tribe, an account of which may be found in vol. i. page 521. But these creatures are generally incapable of passing their life beneath the waters, as their lungs are formed like those of the mammalia, and they are forced to breathe atmospheric air at the surface of the waves. And though they would die if left upon land, their death would occur from hunger and inability to move about in search of food, and in almost every case a submersion of two continuous hours would drown the longest breathed whale that swims the seas.

The Fishes, on the contrary, are expressly formed for aquatic existence; and the beautiful respiratory organs, which we know by the popular term of "gills," are so constructed that they can supply sufficient oxygen for the aeration of the blood. They have not the power, as is sometimes imagined, of separating the oxygen, which, in its combination with certain proportions of hydrogen, composes the element in which they live, but are able to take advantage of the atmospheric air which is contained in the water.

Any reader who happens to possess a globe with gold-Fish can prove, and doubtlessly has proved, the truth of this assertion. It often happens that when the supply of water is insufficient, or the mouth of the vessel too small to permit the air to be absorbed by the water in sufficient volume, the Fish come gasping to the surface, and there swim with gaping mouths, sucking in the air with audible gulps. But if a little water be taken up in a cup or spoon, and dashed back from a little height, so as to cause a sharp splash, or, better still, if a syringe be employed for the same purpose, so as to drive a quantity of atmospheric air into the water; the Fish soon become contented, their anxious restlessness abates, and they quietly swim backward and forward, without displaying any more signs of uneasiness.

The reason that Fishes die when removed from the water, is not because the air is poisonous to them, as some seem to fancy, but because the delicate gill membranes become dry and collapse against each other, so that the circulation of the blood is stopped, and the oxygen of the atmosphere can no longer act upon it. It necessarily follows, that those Fish whose gills can longest retain moisture will live longest on dry land, and that those whose gills dry most rapidly will die the soonest. The herring for example, where the delicate membranes are not sufficiently guarded from the effects of heat and evaporation, dies almost immediately it is taken out of the water; whereas the carp, a fish whose gill-covers can retain much moisture, will survive for an astonishingly long time upon dry land, and the anabas, or climbing perch, is actually able to travel from one pool to another, ascending the banks, and even traversing hot and dusty roads.

The entire shape of these creatures, subjected though it be to manifold variations, is always subservient to the great object of passing rapidly through the ponderous liquid in which they swim, so as to enable them to secure their prey or avoid their enemies. Even in creatures of such different shapes as the sharks, the eels, the salmon tribe, and the flat fish, the capacity for speed is really wonderful, and is in all effected by simple and beautiful modifications of one mechanical principle, that of the inclined plane or screw.

In all Fishes, the power of progression lies in the wonderfully muscular tail with its appended fin, and the creature drives itself forward by repeated strokes of this organ in exactly the same manner that a sailor urges a boat through the water by the backward and forward movements of a single oar in the stern.

To show the power of this principle, I will mention that being on one occasion left

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FINS, SCALES, GILL-COVER, CIRCULATION AND HEARING. with a party of friends on board a fishing barge in a small lake, and deserted by an illconditioned boatman, who refused either to put us ashore or take us to a better fishingground, and so went misanthropically home to his dinner, I called to mind the progression of the Fishes, and straightway became independent of the boatman. After hauling up the anchor, I inserted the butt end of the largest fishing-rod into the head of the rudder so as to form an extempore tiller, and by moving the rudder gently to and fro I was able to propel the barge in any direction and to any distance. We thus traversed the lake at our pleasure, drove the barge ashore at its further extremity, and left the boatman to find it and take it back as he could.

Even the eels and the flat Fishes, with their gracefully serpentine movements, adopt this mode of progression, though it is not so apparent as in the Fish whose bodies are less flexible and accordingly employ more force in the tail itself.

The fins are scarcely employed at all in progression, but are usually used as balancers, and occasionally to check an onward movement. Before proceeding further, I may mention that all the fins of a Fish are distinguished by appropriate names. As they are extremely important in determining the species and even the genus of the individual, and as these members will be repeatedly mentioned in the following pages, I will briefly describe them.

Beginning at the head and following the line of the back, we come upon a fin, called from its position the "dorsal" fin. In very many species there are two such fins, called, from their relative positions, the first and the second dorsal fins. The extremity of the body is furnished with another fin, popularly called the tail, but more correctly the caudal fin. The fins which are set on that part of the body which corresponds to the shoulders are termed the "pectoral" fins; that which is found on the under surface and in front of the vent is called the abdominal fin, and that which is also on the lower surface, and between the vent and the tail, is known by the name of the "anal" fin. All these fins vary extremely in shape, size, and position. The figure on page 198 exhibits all these fins.

The gill-cover, or operculum as it is technically called, is separated into four portions, and is so extensively used in determining the genus and species that a brief description must be given. The front portion, which starts immediately below the eye, is called the "præ-operculum," and immediately behind it comes the "operculum." Below the latter is another piece, termed from its position, the "sub-operculum," and the lowest piece, which touches all the three above it, is called the "inter-operculum." Below the chin and reaching to the sub-operculum, are the slender bones, termed the "branchiostegous rays," which differ in shape and number according to the kind of Fish.

The scales with which most of the Fish are covered are very beautiful in structure, and are formed by successive laminæ, increasing therefore in size according to the age of the Fish. They are attached to the skin by one edge, and they overlap each other in such a manner as to allow the creature to pass through the water with the least possible resistance. The precise mode of overlapping varies materially in different genera. Along each side of the Fish runs a series of pores, through which passes a mucous secretion formed in some glands beneath. In order to permit this secretion to reach the outer surface of the body, each scale upon the row which comes upon the pores is pierced with a little tubular aperture, which is very perceptible on the exterior, and constitutes the "lateral line." The shape and position of this line are also used in determining the precise position held by any species. In comparing the scales taken from different Fishes, it is always better to take those from the lateral line.

The heart of the Fish is very simple, consisting of two chambers only, one auricle and one ventricle. The blood is in consequence cold.

The hearing of Fishes appears in most cases to be dull, and some persons have asserted that they are totally destitute of this faculty. It is now, however, known that many species have been proved capable of hearing sounds, and that carp and other fish can be taught to come for their food at the sound of a bell or whistle. The internal structure of the ear is moderately developed, and there are some curious little bones found within the cavity, technically called otoliths.

The sense of touch seems to have its chief residence in the mouth and surrounding parts, the scaly covering rendering the surface of the body necessarily obtuse to sensation The smell seems to be strongly developed, if it be possible to pronounce an opinion from the size and distribution of the nasal nerves. The brain is very small in these creatures, and from its shape, as well as its dimensions, denotes a low degree of intelligence.

The arrangement of the bones is very curious, and is so complicated that a better idea can be formed by examining the accompanying illustration than by reading many pages of laboured description. The skeleton is that of the common perch.

In the anatomy of the Fishes there are many other interesting structures, which will be described when treating of the particular species in which they are best developed.

THE fishes comprised in the first order, are called by the rather harshly sounding title of Chondropterýgii, a term derived from two Greek words, the former signifying cartilage and the latter a fin, and given to these creatures because their bones contain a very large amount of cartilaginous substance, and are consequently soft and flexible. The bones of the head are rather harder than those of the body and fins.

It is necessary, before entering into any description of the different species, to premise that the arrangement of the fishes is a most difficult and complicated subject, in which no two systematic naturalists seem to agree entirely, I have, therefore, followed the course which has been adopted throughout the whole of this work, and accepted the arrangement given in the catalogues of the British Museum.

The cartilaginous fishes are again subdivided into groups, in the first of which the gills are quite free, and the members of this group are accordingly called by the name of Eleutheropómi, or free-gilled fishes. What quality in the fishes should give birth to such polysyllablic and harsh-sounding names, is not easy to say; but the fact is patent that not even in botany is the scientific terminology so repulsive as in the fishes. I shall endeavour, as far as possible, to avoid this technical language, and to throw the scientific descriptions to the end of the work, as in the two former volumes; and the reader may feel sure when his attention is struck by a long and difficult name, that it is only used in consequence of the exigencies of the occasion.

The first family, of which the common STURGEON is a good and familiar example, are