AND THE LOWER ANIMALS. 211 



marked digestive apparatus provided with a muscular 

 oesophagus and bifid intestine, it is impossible to deny 

 its animality. This peculiar creature has no repro- 

 ductive organ, but, to compensate for its absence, the 

 whole internal surface of the body is endowed with 

 the power of producing germs. The latter, buried in 

 the general internal cavity from which they were pro- 

 duced, are developed sometimes into sporocysts like 

 the first, sometimes into Cercarise. 



The CercariaB, which for a long while were considered 

 to be Infusoria, are like small tadpoles with an oval 

 body, which is provided with a long tail, that serves as a 

 swimming organ. Their organization is complex, and 

 is in process of completion. In addition to a digestive 

 tube, which already reminds one of that of the future 

 Distoma, there are secretory organs, hooklets, &c, but 

 as yet there is no trace of a reproductive organ. 



When their growth is completed, the Cercarias 

 burst the walls of the parent sporocyst, and swim 

 about in the water, where for a certain period they 

 live, like infusorians. Then comes the time for their 

 metamorphoses. They then attach themselves to some 

 mollusk, penetrate the interior of its body, lose their 

 tails and become encysted, almost in the same manner 

 as the Stratiomys, of which we spoke when treating 

 of the metamorphoses of insects. Their organism is 

 now the seat of a process of remodelling, in every way 



comparable with that which we alluded to as occur- 



/■ 



"because they are merely living saccules. For the first he proposes 

 the term Bedies ; for the second, Sporocysts. Moulinie has adopted 

 this distinction, showing at the same time that it is associated with 

 different modes of formation. — " De la Reproduction des Trema- 

 todes endo-parasites." 1856. 



■p 9 



