INTRODUCTION. 



The eyes are usually situated on the sides of the head; 

 but in the Star-gazers, they are on the upper surface. In 

 a variety of the common Gold Fish, known as the Teles- 

 cope Fish, they project so much as to appear to be on 

 stalks. 



Although many blind-fishes are known from the great 

 abysmal depths of the ocean, where the light of day cannot 

 penetrate, very many species occurring in these same 

 immense depths are provided with either normal eyes or 

 even exceptionally large ones ; and, while it is likely that 

 some of these are able to migrate at times into higher 

 levels, it is more probable that they rely usually upon the 

 light emitted either by themselves Tin the case of those 

 supplied with phosphorescent organs) ; or, by the many 

 denizens of the deep, which are known to be phosphores- 

 cent, either wholly or in parts. 



The tongue (where it exists) in fishes, is small, hard 

 and bony ; so that the sense of taste is probably but very 

 feebly developed ; not that it is very necessary, as the 

 majority of them swallow their food either whole or in 

 very large pieces. 



All true fishes possess an internal skeleton. In the 

 great bulk of fishes the Teleosteans (and also in the 

 Lung-Fishes) this skeleton is entirely of a bony nature: 

 but in the Plagiostomes, which include the Sharks and 

 Rays, it is wholly cartilaginous ;* even to the skull itself. 



The fins of fishes are of the greatest importance to 

 them, either in maintaining their balance in, or in assist- 

 ing to propel them through, the water. There are five 

 kinds of fins possessed by the typical groups ; these being 

 termed respectively, dorsal, anal, caudal, pectoral and 

 ventral. The first three are called vertical or unpaired 

 fins, while the remaining two are the horizontal or paired 

 fins. 



In Teleostean fishes, the fins are composed of spines 

 and rays (known also as "hard-rays" and "soft-rays") ; 

 the former being stiff, bony structures, usually connected 

 by a thin membrane ; while the latter are comparatively 



' That is, composed of gristle. 



