ON MONOPYLEPHORUS LIMOSUS. 23 



soidal in form and containing a compact nucleus in the centre. 

 They are not so large as the valvular cells and the cytoplasm 

 stains less well with eosin and is apparently very finely granular. 

 Writes Hat ai, " In only a few among the many specimens that 

 I have observed have I been able to demonstrate valvular cells in 

 the ventral vessel ; but their position is very variable, and they are 

 mostly confined to the anterior part of the body." I am of opinion 

 that Hatai, when writing this, must have had the blood corpuscles 

 before him ; the absence of valves in the ventral vessels is, at least 

 for the present, a common characteristic of the genus. 



3). The intestinal networks form the vascular layer of the 

 intestinal wall. In each segment the network is connected with the 

 dorsal and ventral vessels by median dorsal and ventral intestinal 

 vessels (fig. 23), which are very short and slender and inconstant 

 in number but mostly one dorsally and ventrally for each segment, 

 and constantly present at the points where the anterior ventral 

 integumentary vessels are given off, as will be seen later. 



In segments I and II the alimentary canal does not receive 

 any blood supply from the dorsal vessel, but on the ventral side 

 the ventral vessel itself forms a part of the networks lying in the 

 peritoneum of the gut. 



In segment III a branch starts from the dorsal vessel at about 

 the middle of the segment and runs backwards directly under it. 

 This is the pharyngeal vessel (fig. 9, p.v.), which is a modified 

 dorsal intestinal vessel ; it divides into two, each of which enters 

 the peritoneal connective tissue of the pharyngeal glands at their 

 posterior portion, after which it is again subdivided into many 

 capillaries, which run forwards and downwards and form a not well 

 developed network, uniting at some points directly with that of the 

 preceding segment. 



It is worthy of note that in the genital and following segments 



