144 



THE ANIMAL PARASITES OF MAN 



with rounded edge ; they are frequently of a yellow colour. Their 

 length rarely exceeds a few millimetres.; in some species their size 

 increases exceedingly through proliferation, and then occupy a large 

 portion of 'the body of the intermediary host. 



The REDIAE (figs. 78 and 79), on the other hand, are more cylin- 

 drical and always have a simple intestine of varying length, pro- 

 vided with a pharynx ; they likewise possess a genital orifice situated 

 at the anterior end of the body which serves for the exit of the 

 cercaria originating within them. 



The CERCARIA are very different ; typically they consist of the 



anterior body and the oar-like tail 

 joined to the posterior end (fig, 80). 

 The former, even to the genitals, has 

 the organisation of the adult di- 

 genetic trematodes, and these pecu- 

 . liarities allow the easy recognition 

 of that large group to which the 

 species in question belongs. On 

 the other hand, however, there are 

 also organs that are lacking in the 

 adult form, such as the boring 

 spine in the oral sucker in many, 

 or the eyes situated on the cere- 

 b~al ganglion ; moreover, also, cu- 

 taneous glands (fig. 80), the secre- 

 tion from which forms the cystic 

 membrane. The oar-like tail may 



FIG. 7 8.-Young minal cylinder (r^ be lon g OT sh rt (stump-tailed Cer- 



redia of the Liver dia) of Cercaria caria) or entirely absent ; a fin-like 

 *SK2$& ^nty^nt: membrane may'occur at each side, 

 masses (magni- tine (.), cercaria or the creature may be whorl-like 



fied). (From (c.), germinative , , .,, , . ,-, , < 



Leuckart.) bodies (&.), and and beset with bristles ; its free 



-generative orifice en d ma y be partly split (furcate 



Cercaria), or split to its base (Buce- 



phalus) ; in various forms also the anterior end of the tail is hollow, 

 and has enclosed within it the anterior body, which is otherwise 

 free. The size also of the cercaria belonging to the' different 

 species is very diverse ; in addition to forms swimming in the 

 water that have the appearance of minute milky-white bodies, 

 there are forms which measure as much as 6 mm. in length. 



The encysted forms (fig. 81) are globular or oval, and are sur- 

 rounded by a homogenous membrane, which may be striated or 



