510 ON TWO REMARKABLE SPOROCYSTS, 



A continuation backwards of the cord of cells which forms the 

 rudiment of the pharynx constitutes the rudiment of the short 

 oesophagus. This soon bifurcates posteriorly to form the biramous 

 intestine. In the latter the central cells of the cord become 

 enclosed, as in the case of the pharynx, in a cylinder formed of 

 the peripheral cells. But the latter layer remains very thin, 

 developing into the thin layer of muscle of the wall of the 

 intestine, while the enclosed cells, few and irregularl}^ disposed 

 at first (fig. 23), multiply rapidly, at the same time becoming 

 disposed as a regular epithelial layer (figs. 24-26) bounding the 

 lumen. In the cesophagus the muscular investing laj'er also 

 remains thin, but the enclosed cells give rise to a layer devoid of 

 nuclei, but divided into numerous minute bodies somewhat smaller 

 than the cells of the epithelium of the intestine. 



In Cercaria ao'mata, Schwarze does not refer to the formation 

 of a cleft at the anterior end preceding the development of the 

 unpaired part of the enteric cavity; but describes the latter as 

 appearing in the form of a solid process which only develops a 

 lumen at a later stage by the absorption of the axial cells. In 

 that Cercaria the full development of the forked intestine only 

 takes place after the Cercaria has become encysted, and the entire 

 enteric canal can be functional in the Cercaria stage only very 

 imperfectly, if at all. 



The rudiment of the posterior sucker is distinguishable as a 

 rounded projection on the ventral surface, shortly after the tail 

 begins to be developed ; this consists, like the anterior sucker, 

 of a rounded mass of undifferentiated cells separated internally 

 from the rest of the body cells bj'- a thin membrane. 



When the rami of the intestine first make their appearance, a 

 space — the origin of which has been already referred to — is 

 developed between them. This is the median bladder of the 

 excretory system. At first it has no definite wall, but, later, 

 cells become arranged to form a thin epithelium as in the adult. 



When the cord of cells destined to give rise to the pharynx 

 first becomes differentiated, a mass of cells, as already stated, lies 

 on the dorsal side of it. From the central part of this the first 



