ADAPTATIONS 



333 



of the wasp. The sting-rays (Fig. 194), of which there are 

 many species, have a strong jagged spine on the tail, covered 

 with slime, and armed with broad sawlike teeth. This in- 

 flicts a dangerous wound, not through the presence of spe- 

 cific venom, but from the danger of blood poisoning aris- 

 ing from the slime, and the ragged or unclean cut. 



The poisonous alkaloids 

 within the flesh of some fishes 

 (Tetraodon, Batistes, etc.) 

 serve to destroy the enemies 

 of the species while sacrific- 

 ing the individual. These 

 alkaloids, most developed in 

 the spawning season, pro- 

 duce a disease, known in 

 man as ciguatera. This is 

 rarely known outside of the 

 tropics. 



Many fishes are defended 

 by a coat of mail or a coat 

 of sharp thorns. The globe 

 fishes and porcupine fishes 

 are for the most part de- 

 fended by spines, but their 

 instinct to swallow air gives 

 them an additional safeguard. 

 When one of these fishes is 

 disturbed it rises to the sur- 

 face, gulps air until its capa- 

 cious stomach is filled, and 

 then floats belly upward on 



the water. It is thus protected from other fishes, though easily 

 taken by man. The torpedo, electric eel, electric catfish, and 

 star-gazer, surprise and stagger their captors by means of electric 

 shocks. In the torpedo or electric ray (Fig. 195), of which 

 species are found on the sandy shores of all warm seas, on 

 either side of the head is a large honeycomblike structure 

 which yields a strong electric shock whenever the live fish is 

 touched. This shock is felt severely if the fish be stabbed with 

 a knife or metallic spear. The electric eel of the rivers of 

 Paraguay and southern Brazil is said to give severe shocks to 



FIG. 194. Sting-ray, Urolophus goodei, 

 from Panama. 



