FISHES 



34 1 



developed. Such fish are kept for ornamental purposes, and, as their colour is 

 inherited, great care is taken in breeding them. In addition to the cells with 

 black and red pigment, in most tishes little silvery spots are observable, which lie 

 along the inner side of the scales in the form of small diamond-shaped plates, and 

 at spawning-time produce in many kinds, the stickleback for instance, the most 

 beautiful colours. 



The backbone of a fish consists of only two kinds of vertebra;, those to which 

 ribs are attached and those without ribs. Among the bones of the mouth and 

 throat there are hardly any that may not be provided with teeth. With the 

 exception of those in the snout of the saw-fish, these teeth are never implanted 

 in distinct sockets. Some few fishes, as for instance the sturgeon, have no teeth 

 at all, and in most cases they are in the mouth and throat and not on the jaws. 

 But the number and form of the teeth is in no class of animals subject to so 

 many variations, and it is therefore extremely difficult to exactly divide them 

 into series and define them by name. The fins are mostly expanded like fans 

 by bony or cartilaginous portions of the skeleton forming the so-called fin-rays, 

 the number of which is important in the definition of the species. They are 

 moved by strong muscles and grouped into paired or unpaned fins. The paired 

 fins are named, from their position, either pectorals or pelvics. The pectoral 

 fins are present in almost every fish, and sometimes, as in flying-fishes, are very 

 large. They are always behind the gills, whereas the pelvics may occupy different 

 positions along the body, and in some cases may be wanting altogether. The 

 unpaired fins are the anal, dorsal, and caudal. The anal fin is placed below 

 in front of the tail, the dorsal stands erect on the back, and the caudal fin is at 

 the end of the tail. 



Most fishes are provided with a swim-bladder, which varies much in size 

 and shape, and in many cases is connected with the alimentary canal by an 

 air-tube. It may be compressed or expanded at the will of the fish. Although 

 corresponding in its position in the body to the lungs of other vertebrates, this 

 bladder serves in some of the fishes merely as an additional respiratory organ, 

 for all fish breathe either entirely or partially through gills. These gills, which 

 lie at the back part of the head, consist in ordinary fishes of parallel, comb-like 

 fringes, traversed by many blood-vessels. They may be attached to the gill-arches 

 or to the epidermis, but always lie in the gill-cavity, which is connected with 

 the surrounding parts by the mouth, or the so-called gill-slits at the sides of 

 the head. Fishes impart oxygen to their blood by taking into their mouths the 

 water in which they live, shutting their mouths and expelling the water through 

 the gill-slits, and absorbing the oxygen as it comes into contact with the blood- 

 vessels of the gills. 



Fishes are, as a rule, the most unsociable of vertebrates, and seem to show 

 the least possible mutual sympathy. Their eyes have a very flat cornea, and an 

 exceedingly lai-ge, nearly round, hard, crystalline lens, but some species are blind. 

 Hearing is often supposed to be fairly good, in spite of the absence of external 

 ears ; the sense of smell is in the nasal sacs, mostly situated at the point of the 

 muzzle, which, as being unconnected with the cavity of the mouth, in no way 

 assist in respiration. Fish are provided, however, with one peculiar organ of 



