216 



THE FLUKES 



cysts move by wriggling movements, and absorb nourishment 

 directly through the body wall. When they become over-dis- 

 tended with the cercarise developing within them the wall ruptures 

 and the cercarise are set free in the snail. The cercarise are dis- 

 charged from the mollusc in " puffs," a number being periodically 

 shot into the water. 



Examination of molluscs which were collected in the El Marg 

 canal resulted in finding 17 species of cercariae, among them the 

 cercariae with forked tails and no bulb in the oesophagus, the 



B 



FIG. 67. Larval forms of blood flukes teased from liver of Planorbis; A, 

 sporocyst containing daughter sporocysts; B, daughter sporocysts in liver tissue; 

 C, cercaria. Note forked tail, characteristic of Schistosoma cercarise. (After 

 Leiper.) 



typical form of Schistosoma cercarise (Fig. 67C). Infected mol- 

 luscs may continue to liberate cercarise for several weeks. Leiper 

 later found that S. hcematobium developed only in the species 

 of Bullinus, the cercariae from Planorbis belonging to another 

 species, S. mansoni. In Natal and the Transvaal a small 



