Linton. — C est ode Cysts in Fish 121 



large number of species of our food fishes. Without doubt, 

 therefore, every bluefish, bonito, flounder, mackerel, scup, 

 sea-bass, squeteague, and the like, which has attained mar- 

 ketable size, has taken into its alimentary canal, along with 

 its food, large numbers of larval tapeworms which have 

 been as completely digested and with as much profit to the 

 eater as were the tissues in which the cysts were embedded. 

 Many examples of this sort can be named. Indeed it is 

 worth while to say in passing that if the sharks and skates 

 were to be exterminated almost the entire list of encysted 

 parasites in the flesh and on the viscera of the bony fishes 

 would cease to exist. The list of cestode parasites that are 

 adult in the alimentary canals of teliosts is a very short one. 

 while that of those which are adult in the intestine of the 

 sharks and skates is long. Furthermore, I do not know of 

 any single species of cestode worm that becomes adult in 

 both a selachian and teliost. On the other hand, several 

 examples have come under my observation of species 

 of cestode worms which are confined to a single species 

 of shark. A notable example of this is a large tape- 

 worm which I have found only in the tiger shark. It 

 has been present in large numbers in all the sharks of 

 this species that I have examined, but has not been met 

 with in any other fish. Its life history is as yet not 

 known. In whatever host or hosts it passes its larval 

 stage there can be no doubt that such hosts, together with 

 the larvae of this cestode of the tiger shark, are continually 

 being eaten by other fish both teliosts and selachians. The 

 tiger shark is far from being exclusive in its diet, the list 

 of stomach contents ranging from a pure fish diet to the 

 varied contents of the slop pail of a ship's galley, including 

 even cotton yarn and tin cans. Similar cases could be cited 

 if it were necessary in order to establish the proposition 

 which I wish to make clear, viz., that although the encysted 

 stages of cestode worms may have wide distribution amongst 

 specific intermediate hosts which themselves form the food 

 of an equally large number of species of fish and birds, they 



