334 



EVOLUTION AND ANIMAL LIFE 



herds of wild horses driven through the streams, and similar 

 accounts are given of the electric catfish of the Nile. In 

 tropical seas, the tangs or surgeon fishes (Hepatus) are provided 

 with a knifelike spine on the side of the tail, the sharp edge 

 directed forward and slipping into a sheath. This is a formi- 

 dable weapon when the fish is 

 alive. 



Other fishes defend them- 

 selves by spears (swordfish, 

 spear fish, sailfish) or by saws 

 (sawfish, sawshark) or by pad- 

 dles, (paddlefish). Others still, 

 make use of sucking disks of 

 one sort or another (as in the 

 snailfish, the clingfish, and the 

 goby), to cling to the under 

 side of rocks, or as in the 

 Remora to the bodies of swift- 

 moving sharks. Blind fishes in 

 the caves are adapted to their 

 condition, the eyes being obso- 

 lete, while the skin is covered 

 with rows of sensitive papillse. 

 In similar circumstances sala- 

 manders, crayfishes, and insects 

 are also blind. There are also 

 blind gobies which live in the 

 crevices of rocks and still other 

 blind fishes in the great depths 

 of the sea. 



Some fishes, as the lancelet, lie buried in the sand all their 

 lives. Others, as the sand darter (Ammocrypta pellucida} and 

 the hinalea (Julis gaimardi), bury themselves in the sand at 

 intervals to escape from their enemies. Some live in the 

 cavities of tunicates or sponges or holothurians or corals or 

 oysters, often passing their whole lives inside the cavity of one 

 animal. Many others hide themselves in the interstices of 

 kelp or seaweeds. Some eels coil themselves in the crevices 

 of rocks or coral masses, striking at their prey like snakes. 

 Some sea-horses cling by their tails to gulf weed or sea- wrack. 

 Many little fishes (Gobiomorus, Carangus, Psenes) cluster under 



FIG. 195. Torpedo or electric ray, 

 Narcine brasiliensis, showing elec- 

 tric cells. 



