168 



METAZOAN PHYLA 



(Fig. 81), a fluke which lives as an adult in the bile ducts of the liver of 

 man, dog, and cat, and is found in China and Japan. In addition to 

 the firm leathery cuticle, the absence of cilia, and the presence of suckers, 

 all of which represent adaptations to a parasitic mode of existence, this 

 form in its adult condition is to be contrasted with a planarian in the 

 absence of eyespots and in the more highly developed reproductive 

 system. The single excretory pore lies at the extreme posterior end of 



-Ora/ sucker 

 -Pharynx 



'Merve center 



Gen/fa/ 

 ,pore 



Excrefory 

 ■/■ube 



Sem/no// 

 recepfiPrc/e 



Lauren's 



Ccrncr/ 



Testes 



Enferon 

 Ven traf sucken 



Yolk gr/an(^S 



_ Seminal 

 vesicle 



Uterus 



Yolk c/uct 

 Ovary 



Vas efferens 



£xcretony 

 pore 



Fig. 81. — Clonorchis sinensis Cobbold. {Redrawn from Hegner, Root and Augustine, 

 "Animal Parasitology," after Faust.) Dorsal view, showing internal structure. X 8. 



the body. Added to the female organs is a sheM gland which secretes a 

 substance that hardens the shells of the eggs (Fig. 82). Almost all 

 trematodes pass through a complicated life cycle spending the early part 

 of their life in some snail or related animal before entering the host in 

 which they mature. There may be three or four different hosts required 

 for the complete cycle. Clonorchis develops first in a snail, then in a 

 fish, before entering man. 



