54 Adaptations of Fishes 
Spines of the Sting-ray.—JIn 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. 88.—Common Filefish, Stephanolepis hispidus (Linneus). 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 globefishes (Tetraodontide), 
the filefishes (Monacanthus), and in some related forms, while 
members of other groups (Batrachoidid@) 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 
