PLATYHELMIA. 



37 



chamber, it becomes a sporocyst. The ciliated ectoderm-cells 

 are lost, and the body gradually becomes an elongated and rather 

 irregular sac. Its wall is covered externally with a cuticle, below 

 which are feebly developed muscle-fibres, within which is a layer 

 of epithelium lining the body-cavity. Several excretory funnels 

 are present in the body-wall, and the eye-spots, separated from 

 each other, can still be recognised. The sporocyst may multiply 

 by transverse fission, and it produces asexually within it a number 



Fig. 8. DEVELOPMENT OF DISTOMA (from Glaus, partly after Leuckart). 

 a, Free swimming ciliated embryo: b, the same contracted, with 

 rudimentary gut, D, germinal cells, Ov, and excretory funnels, Ex: 

 d, redia; 0, mouth; Ph, pharynx; D, intestine; Ex, excretory tubule ; 

 C, contained cercarise: e, free cercaria ; S, ventral sucker ; D, intestine; 

 Ex, excretory tubule; the little circles in the body represent cysto- 

 genous cells. 



of the next, or redia stage, in the following manner : The body- 

 cavity contains a large number of germinal cells, partly those of 

 the free embryo, partly budded off from the lining epithelium, 

 lying loosely within it. These become aggregated into small 



