CLASS V. PISCES. 421 



Scales are composed of two substances, one resembling horn in its texture, and the other of a 

 harder and bone-like nature ; they are generally attached to the skin by the anterior edge, and con- 

 sist of numerous concentric lamina?, secreted by the skin, tlie smallest of Avhieh are first formed. 

 Certain scales, forming a continuous series, in a slightly-waved line from the head to the tail of 

 the fish, are pierced in or near their center, and furnished with a tube through which a slimy 

 matter is poured, which serves to lubricate the body of the animal. This series of tubes forms 

 a line visible on the sides of the body, and which is termed the lateral line. 



The structure, form, and position of the scales of fishes are very variable, and have furnished 

 M. Agassiz, in his celebrated Mecherches sur Ics Poissons Fossiles, with characters for a new 

 classification of these animals. 



As regards the senses, the organs of which are as usual placed upon the head, those of Taste 

 and Touch appear to be but slightly developed in fishes. AVhen we find the tongue thickly 

 covered with teeth, as is often the case, and used as an organ of prehension, and when we con- 

 sider the rapid manner in which the food is swallo-wed, it would certainly appear that their sense 

 of taste is very slight. The sense of touch is probably most developed in the cirrhi attached to the 

 mouth of those which possess them. The long filaments with which the fins of some fishes are fur- 

 nished also perhaps serve, through the sense of touch, to indicate the vicinity of weeds, or other 

 objects in the water. The Eyes are differently situated in the various species of fishes, in accord- 

 ance with their habits; for the most part they are placed laterally, and in some, those that live 

 at the bottom of the water, we find them directed upward. In some of the species of sharks 

 they are situated at the end of an elongated lateral process on each side of the head. The Sight 

 in fishes is acute ; the range of vision, however, is probably somewhat limited. The eyes, which 

 are furnished with a spherical lens, are generally large, but in some species they are very small, 

 while others are destitute of them. Although fishes appear not to possess certain portions 

 of the auditory apparatus observed in animals of a higher grade, they nevertheless have the 

 sense of Hearing in some degree. There are reasons for the belief that the sense of Smell in 

 fishes is tolerably acute ; their olfactory nerves are of large size, and disposed over a consider- 

 able extent of surface. 



By far the greater number of fishes are of carnivorous and predacious habits, attacking and 

 destroying indiscriminately all the weaker inhabitants of the water, such as insects, worms, Crus- 

 tacea, and mollusca, and devouring with avidity the smaller individuals of their own class. As 

 there is no instinct to restrain the community of fishes, so there is no moral law to regulate it. 

 Appetite and might are the only measures of conduct alike with the shark and the minnow. 

 There are a few, however, which feed upon vegetable substances, and we find the stomach modi- 

 fied accordingly, as in other animals. 



The Sexes of fishes, if we except the sharks and rays, offer no very decided external characters 

 by which they may be distinguished ; as in the higher animals, however, observes Mr. Yarrell, 

 " the respiratory organs occupy more space in the males than in the females ; and, on the other 

 hand, the abdomen is larger in the females than in the males ; the males may therefore be known 

 from the females by their somewhat sharper or more pointed head, the greater length of the 

 gill-cover, and the body from the dorsal fin downward being not so deep compared with the 

 whole length of the fish." 



The reproductive organs of fishes are in the generality of the species of a more simple nature than 

 is observed in the higher orders of the Vertebrata, consisting, toward the season of producing 

 their young, of two elongated oval lobes of roe, one on each side of the body, placed between the 

 ribs and the intestinal canal ; the lobes in the female, called hard roc, contain a very large num- 

 ber of roundish grains, called ova or eggs, which are inclosed in a delicate membraneous tunic or 

 bag, reaching to the side of the anal aperture, where an elongated fissure permits egress at the 

 proper time. In the males the lobes of roe are smaller than in the females, and have the ap- 

 pearance of two elongated masses of fot, which are called soft roe or milt ; they remain firm, how- 

 ever, till the actual season of spawning, when they become by degrees more and more fluid, and 

 the whole is ultimately voided by small portions at a time, under slight abdominal pressure. The 

 artificial breeding of fishes, now extensively practiced in Europe and America, is founded upon 



