THE TREMATODA 



77 



In D. ovocaudatum, from the oral cavity of Rana esculenta, the 

 miracidium is deprived of cilia, for the eggs are eaten by the inter- 

 mediate host (Planorbis). 



Amphistomum subclamtum lives in the intestine of frog, etc. ; 

 the miracidium enters species of Planorbis; the cercaria leaves this 

 first host, swims about for a few hours, falls to the bottom and 

 encysts. This happens throughout the summer ; and the cysts 



FIG. XVIIL The Life-history of D. macrostomum, Rud. (After Heckert.) 



1. Outline of the adult fluke, parasitic in song-birds, a, mouth surrounded by the oral 

 sucker ; b, pharynx ; c, ventral sticker ; d, genital pore. 



2. The iniracidiuni which is hatched in the stomach of the snail. 



3. The intermediate host, Succinea amphibia, crawling on a leaf (in), (nat. size), a, the 

 cavity of the right tentacle is occupied by Leucochloridium. In some cases both tentacles will 

 be similarly occupied. 



4. The sporocyst, in various stages of growth, giving rise to a much-branched tube (D), 

 the ends of some of the branches becoming enlarged. 



5. A fully-grown I^eucochloridium paradoxum the elaborate sporocyst which occupies 

 the body cavity of the snail. One terminal branch is fully developed ; two others are 

 nearly so, and are banded with greens and browns. 



are devoured by insect larvae, which in their turn are eaten by 

 the final host, the frog, during winter (Looss, 30). Or, according 

 to Lang, the encystment occurs on the skin of frogs and newts, 

 and the cysts are swallowed with the skin when moulting occurs. 

 In this way a gradual passage is formed between cases with and 

 without a second intermediate host. 



Further Remarks upon the Class Trematoda. The animals included 

 in this class are characteristically parasitic, and the two orders, 



