THE FISHES 



173 



the touch. The herring and shad are examples, as also the 

 salmon and trout. Some live in the great depths of the 

 sea, even five miles below the surface. These are very soft 

 in body, being under tremendous pressure. They are inky 

 black for the sea at that depth seems black as ink and 

 most of them have luminous spots which give them light 

 in the darkness. Some species have the forehead luminous, 

 like the headlight of an engine. Most of these deep-sea 

 fishes are very voracious, for there is nothing for them to 

 feed on save their neighbors. 



166. The pike, sticklebacks, etc. Several small orders 

 stand between these soft-rayed, smooth-scaled fishes and 



FIG. 104. The blindfish and its parentage. A, Dismal Swamp fish (Chologaster 

 amtus), the ancestor of (B) Agassiz's cave fish (Chologaster agassizi) and (C) 

 cave blindfish (Typhlichthys subterr emeus). 



the form, like the perch and bass, which has many spines in 

 the dorsal fin. Among these transitional forms is the pike 

 (Fig. 105) long, slender, circumspect, and voracious, lying 

 in wait under a lily-pad ; the blindfish, which lost its eyes 

 through long living in the streams of the great caves ; the 

 stickleback, small, wiry, malicious, and destructive, steal- 

 ing the eggs and nibbling the fins of any larger fish; 

 the sea-horse, often clinging with its tail to floating 



