194 Natural History of Entozoa. 



Fig. 7 g represents a fully developed cercaria, in which a 



Kg. V. 



is the oral sucker, b pharyngeal bulb, c oesophagus, dd two 

 alimentary cceca, e ventral sucker, g g water vascular system, 

 consisting of two excretory ducts, / a contractile vesicle by 

 which the ducts communicate with the external surface, h the 



Fie. 8. 



tail, with fringe ii. Before this cercaria becomes sexually 

 mature it passes through the stage represented in Fig. 8, having 



