568 



DEVELOPMENT OF ENTOZOA. 



(fig. 309) having a sac-like body clothed with cilia and capable 

 of motion ; within the anterior part of which is to be observed 

 an elongated stomach s, whilst the posterior portion of the 

 cavity is occupied by a number of bodies a, having a general 

 resemblance to itself, which are produced from it by a process 

 of internal gemmation. These, when mature, burst forth 

 from the containing cyst, and develope themselves into 

 worms (fig. 310) not very unlike the preceding in general 

 form and organization, though differing from them in some 

 important particulars; and in their turn they produce, by 

 internal gemmation, a fresh brood of bodies much more 

 dissimilar to themselves. These, when set free in due time, 



Fig. 309. 

 GRAND-NURSE OF CEHCARIA. 



Fig. 310. 

 NURSE OF CERCARIA. 



develope themselves into a form which has long been known 

 as the Cercaria (fig. 311), and which has a tadpole-like body 

 with a large sucker a in its middle, a triangular head, a long 

 tail by the motion of which it swims, and various viscera c 

 in its interior. The Cercarise attach themselves by means of 

 their sucker to the bodies of the Lymnseus, and then begin to 

 undergo an important metamorphosis. The tail, being now 

 useless, falls off ; the animal becomes invested with a mucous 

 substance, within which it lies encysted like a chrysalis 

 within its cocoon ; and, on its emergence from this it presents 

 itself as a Distoma, which is ready by the performan.ee of the 

 true generative process, to set in renewed operation the whole 



