26 ELEMENTS OF COMPARATIVE ZOOLOGY. 



The "blind fish of Mammoth Cave should be mentioned 

 here. In this form a life in total darkness has resulted in 

 the degeneration of the eyes, which are buried beneath the 

 skin. 



The savage, swift-swimming pike, pickerel, and muska- 

 longe, the latter reaching a length of eight feet, are, with 

 one exception, confined to America. They are noted for 



FIG. 4. Herring (Clupea harengus). 



their voracity, and have been termed " mere machines for 

 the assimilation of other organisms." 



Among the marine members of the order are the herrings, 

 shad, menhaden, fishes of great importance to man, both 

 as food and for the oil and fertilizers which are made from 

 them. They occur in large schools, and afford food for 

 numerous predaceous fishes. 



Differing from the forms already mentioned are those 

 which may be grouped together as eels, fishes with elongate 

 bodies and without ventral fins. Most of the species are 

 marine, and those which live in fresh water go to the sea to 

 spawn. All are voracious creatures, and one South Ameri- 

 can species has marked electrical powers. 



ORDER II. ANACANTHINI. 



These have the gills comb-like (p. 24) ; the dorsal, anal, 

 and ventral fins without spines; the ventral fins, when 



