

Development 



89 



the water. This discharge occurs quite independently of the 

 passage of ftrces by the snail. 



In Bilharzia as in all digenetic trematodes the terminal phase 

 of development in the intermediate host is the cercaria, and this 

 alone is the infective staffc. 



Fig. 44. — Section of hepatic gland of infected Planorhis boissyl, showing 

 extent of atrophy of tissue. 



Differentiation of Cercarl^. 



A cercaria consists typically of two parts, viz., body and tail. 

 The tail is always discarded when the body enters its final or 

 definitive host. It is therefore a purely larval structure. The 

 body, on the other hand, is actually the undeveloped adult, many of 

 the adult characters being almost undifferentiated. In addition to 

 these the cercarial body may have other structures which have 

 been serviceable during its growth in the molluscan host, but which 



