ANATOMY AND DEVELOPMENT OP PERIPATUS OAPESfSiS, 227 



tract, without a mesentery. The structure of the walls of 

 the stomach has not hitherto been very satisfactorily de- 

 scribed. 



The connective tissue and muscular coats are extremely 

 thin. There is present everywhere a peritoneal covering, and 

 in front a fairly well-marked though very thin layer of muscles 

 formed of an external circular and an internal longitudinal 

 layer. In the middle and posterior parts, however, I was 

 unable to recognise these two layers in section; although in 

 surface view Grube found an inner layer of circular fibres 

 and an outer layer formed of bands of longitudinal fibres, 

 which he regards as muscular. 



The layer supporting the epithelium is reduced to a base- 

 ment membrane. The epithelial part of the wall of the 

 stomach is by far the thickest (fig. 20), and is mainly com- 

 posed of enormously elongated, fibre-like cells, which in the 

 middle part of the stomach, where they are longest, are 

 nearly half a millimetre in length, and only about "006 mm. 

 in breadth. Their nuclei, as seen in fig. 20, are very elon- 

 gated, and are placed about a quarter of the length from the 

 base. 



The cells are mainly filled with an immense number 

 of highly refracting spherules, probably secretory globules, 

 but held by Grube, from the fact of their dissolving in 

 ether, to be fat. The epithelial cells are raised into nu- 

 merous blunt processes projecting into tlie lumen of the 

 stomach. 



In addition to the cells just described there are present in 

 the anterior part of the stomach a fair sprinkling of mucous 

 cells. There are also everywhere present around the bases of 

 the columnar cells short cells with spherical nuclei, which are 

 somewhat irregularly scattered in the middle and posterior 

 parts of the stomach, but form in the front part a definite 

 layer. I have not been able to isolate these cells, and can 

 give no account of their function. 



The rectum extends from the end of the stomach to the 

 anus. The region of junction between the stomach and the 



