228 



THE ANIMAL PARASITES OF MAX 



rarely exceeds a few millimetres ; in some species their size increases 

 exceedingly through proliferation, and they then occupy a large portion 

 of the body of the intermediate host. 



(3) The REDI.E (figs. 132, 133), on the other 

 hand, are more cylindrical and always have a 

 simple intestine of varying length, provided 

 with a pharynx ; they likewise possess, situated 

 near the circular ridge, a " birth pore " which 

 serves for the exit of the cercariae originating 

 within them. 



(4) The CERCARI.E 1 are veiy different; typi- 

 cally they consist of the anterior body and the 

 oar-like tail at the posterior end (fig. 134). The 

 former, even to the genitalia, has the organiza- 

 tion of the adult digenetic Trematodes, and 

 thus allows the easy recognition of at least the 

 characters 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, in many, the 

 boring spine in the oral sucker, or the eyes 

 situated on the cerebral ganglion ; moreover, 

 also, cutaneous glands (fig. 134), the secretion of 

 which forms the cyst membrane. The oar-like 

 tail may be long or short (stumpy-tailed cer- 

 caria) or entirely absent ; its free end may be 

 partly split (furcate cercaria), or split to its base 

 (bncephalns} ; in various forms also the an- 

 terior 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 cercariae (fig. 135) are globular 

 or oval, and are surrounded by a homogeneous 



FIG. 134. Cercaria of 

 Fasciola hepatica ; the cuta- 

 neous glands at the side of 

 the anterior body. Mag- 

 nified. (After Leuckart.)i^ 



FIG. 135. Encysted cer- 

 caria of Fasciola hepatica. 

 Magnified. (After Leuck- 

 art.) 



1 The cercaria is the characteristic larval stage of the Trematodes, and corresponds to a 

 "cysticercus or cysticercoid, though there is the important difference that the cercaria has an 

 enteric cavity. According to some observers the enteron is represented by the frontal sucker 

 of some Cestodes, and by the rostellum of the majority of others. 



The sporocyst and redia are regarded as intercalated stages, -viz., as cercariae exhibiting 

 padogcnesis, i.e., development of young by a parthenogenetic process fn m individuals (i.e. t 

 cercarise) not yet adult. 



