No. 3.] STUDY OF STENOSTOMA LEUCOPS O. SCHM. 299 



which leads to the mouth of the adult. Here the cone-shaped 

 depression joins the pharynx, and there is thus formed between 

 them the distinct line of demarcation which was mentioned 

 above. 



As Wagner has also proven that the pharynx of Microstoma 

 lineare is developed from the parenchyme and not from the integ- 

 ument, it may be inferred with safety that the pharynx of the 

 Rhabdocoels is developed from mesoblast which is potentially 

 hypoblastic, and not from the epiblast. 



Summary of Results. 



I. The muscular layer of the integument is composed of cir- 

 cular and longitudinal fibres. The circular fibres lie next to the 

 epithelial cells. The nuclei of the epithelial cells divide by 

 karyokinesis. 



II. The parenchyme is made up of a network and a perivis- 

 ceral fluid which fills the spaces in the network. The network 

 is formed by the fusion of individual cells which are connected 

 by branching and anastomosing processes, and are separated by 

 inter-cellular vacuoles. 



III. The distal ends of the epithelial cells of the intestine 

 are not ciliated, but are provided with long, slender, retractile, 

 cilia-like, protoplasmic processes by means of which they take 

 up the food material directly. 



IV. The pharyngeal apparatus is divided into two parts, 

 "cone-shaped depression" and "pharynx." The "cone-shaped 

 depression " is developed from a depression of the ectoderm, 

 and is homologous with the entire pharyngeal apparatus of the 

 Polyclads. The "pharynx" is formed from the mesenchyme, 

 and is homologous with the Triclad pharynx, 



V. The smaller, branching limb of the water vascular tube 

 extends its fine branches to the posterior extremity of the body 

 and lies dorsal to the larger limb which opens to the outside at 

 the posterior end of the body. 



VI. The ciliated pits are formed from simple depressions of 

 the integument. Their inner surfaces are surrounded by the 

 anterior ends of the brain lobes. The structure of their walls is 



