FLATWORMS 



Fig. 11.15. Developmental staa;es 

 of C/onorchis sinensis. A, embry- 

 onated egg, containing a well- 

 developed miracidium. B, mira- 

 cidium emerging from the egg 

 capsule. C, miracidium. D, ma- 

 ture sporocyst from the liver of 

 a snail, containing rediae. E, 

 redia with developing cercariae. 



F, cercaria. G, metacercaria dis- 

 sected from its cyst in the skin 

 of a fish. A, B, and C are en- 

 larged approximately ten times as 

 much as the other figures, and F 

 is somewhat more enlarged than 



G. (Adapted from D. L. Belding, 

 Textbook of Clinical Parasilolooy, 

 second edition, copyright 1952 

 by Appleton-Century-Crofts, Inc., 

 printed by permission; A through 

 F after Faust and Khaw, F after 

 Yamaguti, C after Hsii and Khaw.) 



adult. Thus, from each zygote, many individuals ultimately result. It must 

 be borne in mind, however, that in order to produce the next larval genera- 

 tion, each stage must, within a certain time limit of survival, encounter and 

 successfully penetrate the appropriate host. The chances against the survival 

 of all the offspring of a single worm are astronomical, and so the species does 

 not indefinitely increase in numbers of individuals. 



The exact nature of the multiplicative processes occurring in the larval 

 stages of digenetic trematodes has been the subject of investigation and de- 



331 



