35 



pallial cavity. The intestine leaves the stomach dorsally 

 and anteriorly and lies close to the surface until the renal 

 organ is reached. It then plunges underneath the latter 

 (though still on the surface of the digestive gland and 

 outside the pericardium), and reaches the pallial cavity. 



It is now some distance away from the oesophagus 

 and ascends into the wall of the pallial cavity, taking a 

 course along the right side at the extreme edge. In the 

 female this distal portion, the rectum, is compressed by 

 the oviduct. The rectum terminates in a conical protu- 

 berance at the end of which the anus is situated (fig. 8, 

 An.). With the exception of glandular walls, no special 

 anal or rectal glands are present. 



Histology of the Alimentary Canal 

 and related Organs. 



A detailed account of the histology of the whelk's 

 tissues would be far beyond the limits of this Memoir. 

 Only some of the more typical and important structures 

 will be referred to here.* 



The Pharynx. — The pharynx in life has a peculiar 

 pink colour, due to its muscular wall. In sections one 

 finds the lumen of the gut lined by a layer of deep 

 epithelial cells. As a matter of fact, the lining of the 

 gut is very similar throughout its length, and the same 

 kinds of cells are found in the epithelium, viz.: — 

 (1) Ciliated cells, (2) Eosinophilous cells, (3) Gland cells. 

 Whatever may be the function of the two latter types, it 

 is interesting to notice that they occur throughout the 

 whole length of the gut from pharynx to rectum. 



The ciliated cells (fig. 24, CI. c.) are typical tall 



* The author intends to publish shortly a series of papers dealing 

 with Molluscan Histology. 



