78 



PLATYHELMINTHES 



Clonorchis sinensis^ found in China and Japan and recently- 

 introduced into the U. S., infests the liver of man, cats, dogs and 

 pigs. It is generally leaf-like in shape and has two suckers. The 

 eggs hatch in the operculate snail Bithynia and the cercariae leave 

 the snail and encyst in thirty-four reported species of fresh water fish. 

 Man and the other mammalian hosts acquire the infection by 

 eating uncooked infected fish. 



Fig. 34. Cercaria and adult of Cryptocotyk lingua. (Courtesy of H. W. Stunkard.) 



In Cryptocotyle lingua., studied by Stunkard,-* we have an in- 

 teresting illustration of what may occur with introduced species. 

 The snail, Littorina litto?-ea, brought with ballast to New Brunswick, 

 Canada, in 1855, is supposed to have carried with it the cercariae of 

 Cryptocotyle lingua. The metacercariae of C. lingua occur in 

 marine fishes, chiefly the cunner, and adults are found in the intes- 

 tines of fish-eating birds and mammals. Four related species have 

 been shown experimentally to be infective for man. (Figure 34.) 

 It is possible that this form, readily collected at the Marine Biologi- 

 cal Laboratory, Woods Hole, Mass., may be used inland just as the 

 nematode Metoncholaimus pristiurus is now being shipped to dis- 

 tant points. (See page 98.) 



Class 3. Cestoda. Type — Taenia solium. — The common pork 

 tape worm lives in the alimentary canal of man as an adult. Its 

 secondary host is the pig. The adult tape worm has a well-developed 



* Stunkard, H. W. 1930. The life history of Cryptocotyle lingua. Jour. Morph. 

 and Physiol., vol. 50, pp. 143-183. 



