l82 



Adaptations of Fishes 



Spines of the Sting-ray. In all the large group of sting- 

 rays the tail is provided with one or more large, stiff, barbed 

 spines, which are used with great force by the animal, and are 

 capable of piercing the leathery skin of the sting-ray itself. 

 There is no evidence that these spines bear any specific poison, 

 but the ragged wounds they make are always dangerous and 

 often end in gangrene. It is possible that the mucus on the 

 surface of the spine acts as a poison on the lacerated tissues, 

 rendering the wound something very different from a simple cut. 



Protection Through Poisonous Flesh of Fishes. In certain 

 groups of fishes a strange form of self-protection is acquired by 



FIG. 136. Common Filefish, Stephanolepis hispidus (Linnaeus). Virginia. 



the presence in the body of poisonous alkaloids, by means of 

 which the enemies of the species are destroyed in the death 

 of the individual devoured. 



Such alkaloids are present in the globe fishes (Tetraodontida:'), 

 the filefishes (Monacanthus), and in some related forms, while 

 members of other groups (Batrachoidida) are under suspicion in 

 this regard. The alkaloids produce a disease known as cigua- 

 tera, characterized by paralysis and gastric derangements. 

 Severe cases of ciguatera with men, as well as with lower 

 animals, may end fatally in a short time. 



The flesh of the filefishes (Stephanolepis tomentosus), which 



