312 WILLIAM A. HASWELL. 



becomes affected by staining agents much more strongly 

 than the rest; these are probably of the nature of unicellular 

 digestive glands. External to this there is merely a thin 

 peritoneal layer without any muscular fibres. 



The stomach and intestine invariably contain a quantity 

 of miscellaneous granular particles which are so finely com- 

 minuted as to afford no clue to their nature. 



Body-cavity. 



There is an extensive body-cavity sending a prolongation 

 into the head. In Histriobdella, Foettinger describes this 

 cavity as lined by a ccBlomic epithelium having the usual 

 relations of such a membrane, a splanchnic layer covering 

 the surface of the digestive canal, and a somatic layer lining 

 the inner surface of the body-wall. But such a description 

 does not give a correct idea of the coelomic wall, at all 

 events in Stratiodrilus. Covering the stomach and intestine 

 throughout is the splanchnic layer of coelomic epithelium, a 

 thin layer of flattened cells with small nuclei. But the soma- 

 topleure remains in a vei-y primitive condition. Closely 

 applied to the inner surfaces of the dorsal and ventral longi- 

 tudinal bands of muscle is a single layer of cells, the proto- 

 plasm of which is seen in the best series of sections (fig. 3) 

 to be completely continuous with the muscle substance of the 

 fibres. These cells, which are obviously the cells by means 

 df which the muscular fibres have become formed, are also 

 the only representatives of the somatic layer of the meso- 

 derm. This condition of things corresponds exactly to what 

 has been described by Fraipont as occurring at a certain 

 stage in the development of Polygordius. In the latter 

 the somatic layer of the coelomic epithelium subsequently 

 becomes formed by the division of this single layer into two; 

 in Stratiodrilus the embryonic condition remains permanent. 



There are no mesenteries of any kind, the Avail of the 

 stomach and intestine being simply fused on the dorsal side 

 with the ectoderm as described by Foettinger. In this 



