484 



FISH. 



cannot bear to be frozen without destroying their 

 vitality ; but the spawn of frogs can, and probably 

 so can that of fishes. This influence of changes of 

 temperature, especially cold, on fishes, is a subject 

 well worthy of investigation both in a natural history 

 point of view and in an economical one. It has been 

 found a great improvement in the quality of salmon 

 in the London market, to have them packed in ice ; 

 but if we could freeze them alive and thaw them out 

 as we wanted them, it would be much better. The 

 subject, however, we cannot pursue farther. 



Organs of Nutrition. In fishes, as in all vertebrated 

 animals, these consist of a mouth, a gullet, a stomach, 

 or an intestinal canal. The mouth is, among fishes, 

 the only instrument which they have for catching 

 their food ; for though there are many curious ap- 

 pendages to the bodies of some of them, of which the 

 uses are little, if at all, known, it is not probable that 

 any of them assist in the actual capture, and none of 

 those appendages is in its structure fitted for cap- 

 turing. Some of the ground fishes, the common 

 angler, for instance, are said to make use of the fila- 

 ments with which they are furnished, for the purpose 

 of enticing other fishes within their reach ; and the 

 chaetodon rostratus, of the fresh waters of India, is 

 said to be a very skilful marksfish, in shooting flies 

 by means of drops of water. We shall give the 

 account of this in the language of Dr. Shaw ; but we 

 do not vouch for all the circumstances, which we 

 suspect are rather too clever for a fish. " When," 

 says the doctor, " it observes one of these (an insect) 

 either hovering over the water or seated on some 

 aquatic plant, it shoots against it from its tubular 

 snout a drop of water, with so sure an aim as gene- 

 rally to lay it dead, or, at least, stupified on the sur- 

 face. In shooting at a sitting insect, it is commonly 

 observed to approach within the distance of from four 

 to six feet before it explodes the water. When kept 

 in a state of confinement in a large vessel of water, 

 it is said to afford high entertainment by it dexterity 

 in this exercise ; since, if a fly or other insect be 

 fastened to the edge of the vessel, the fish imme- 

 diately perceives it, and continues to shoot at it with 

 such admirable skill as very rarely to miss the mark." 



The mouth of fishes varies much more in size and 

 shape than that of vertebrated animals of any other 

 class ; generally speaking, its opening is horizonal, 

 and across the mesial plane, with its action, or opening 

 and shutting, in the direction of that plane ; but the 

 flat fish form an exception to this, as will be more 

 particularly explained in describing them. The lips 

 are not often well formed, but some are firm and 

 fleshy, and completely surround the mouth, while 

 others are covered with plates of bony matter, which 

 fold over each other. Lips of this description often 

 increase the dimensions of the mouth, as they are 

 capable of extension and folding up. Both jaws are 

 moveable, though the chief motion is in the under 

 one, and the gape is very wide : there are few fishes 

 in which they are both of equal length ; sometimes 

 the upper and sometimes the under is the largest, and 

 in not a few instances one or both of the jaws are 

 extensile, or capable of being projected forward be- 

 yond the length which they have in a state of repose. 

 The teeth of fishes are exceedingly varied, and situ- 

 ated in all imaginable parts of the mouth, and 

 sometimes outside that opening altogether. Among 

 the mammalia, the number of teeth in the same 

 species, or even in the same genus, is generally con- 



stant ; but it is very different among fish. The teeth 

 are often so numerous that it is difficult to count them, 

 especially as they occupy so many different positions. 

 The jaws are not exclusively employed to support 

 these organs, as in quadrupeds ; the tongue, the 

 palate, the throat, being often furnished with them. 

 In the saw-fish, the teeth are inserted on each side of 

 its flattened and projecting snout In the genus 

 sparus, the front teeth resemble those of the human 

 species. They are provided with fangs, which are 

 contained in alveoli. In many fishes, the teeth arc 

 formed* of processes of the jaw-bones covered with 

 enamel. Those of the shark tribe adhere merely to 

 the gums, or, at least, to a firm cartilaginous sub- 

 stance which covers the jaw. They are not formed, 

 as in the mammalia, by the addition of new layers, 

 one within the other, but apparently in a manner re- 

 sembling the formation of bone. They are at first 

 soft and cartilaginous, and pass, by successive grada- 

 tions, into a state of hardness and density not inferior 

 to that of ivory. In the skate, the teeth consist of an 

 assemblage of tubes, covered externally by enamel, 

 and connected to the jaw by a softer substance, which 

 probably sends processes or vessels into those bony 

 tubes. The teeth of fishes are in general bent in- 

 wards, to enable them to retain their prey. As few 

 fishes masticate, they have seldom any teeth which 

 resemble grinders, although those which live on the 

 harder shell-fish have teeth fitted for triturating them. 

 In the classification of fishes, the teeth furnish several 

 important characters, which are little liable to varia- 

 tion. In the shark tribe, in particular, the teeth 

 exhibit many remarkable differences in form, suf- 

 ficient, in the absence of other characters, for the 

 discrimination of the species. The form of the teeth 

 and their arrangements are not less various than the 

 places on which they are situated. Generally speak- 

 ing, they are individually in the form of cones, or they 

 are hooked. If these are placed in several rows, 

 they* are sometimes called carded teeth, because they 

 bear a resemblance to the teeth of the instruments 

 used in carding wool and other matters ; if they are 

 very small, numerous, and thickly set, they are called 

 velvety (en velours) ; and if long and close they are 

 called brushes. Sometimes, however, the individual 

 teeth are too minute for being seen, though they may 

 be felt as a sort of granular roughness upon the sur- 

 face. In this case they are said to be asperities. 

 Though the teeth of those species which feed upon 

 fuel, and other vegetable products of the sea, are 

 adapted for biting off or dividing those products, and 

 some of the teeth of the sharks are capable of dividing 

 and tearing in a dreadful manner, yet there is no 

 provision in the mouth of a fish by means of which 

 mastication or chewing can be performed. Indeed 

 this is an operation exclusively confined to the mam- 

 malia, which accordingly are the only animals which 

 have a grinding or a lateral motion in the jaws ; and 

 thus all fishes are obliged to swallow their food in the 

 same manner in which it is at first taken into the 

 mouth. The lips, in the bony fishes especially, have 

 no muscles by means of which they can be closed and 

 compressed so as to assist in the act of swallowing, 

 though they have often masses of considerable size to 

 swallow. Instead of this they have a peculiar ap- 

 paratus, to which we made some allusion when 

 speaking of the progress of the water in breathing. 

 Behind the front teeth, or those in the anterior part 

 of the jaw and the vomer, there is a reduplication of 



