ON MONOPYLEPHOKUS LIMOSUS. 



17 



muscle fibres. The outermost layer is that of the chloragogues 

 which mostly commence in segment VI, but often in the preceding 

 segment. The rectal bulb is lined by the ectoderm and its wall 

 consists of five layers corresponding to those of the body wall. 



The chloragogue cells are mainly ovoid or pear-shaped with 

 the thicker end directed towards the body cavity. The cytoplasm 

 is more or less granulated and the nucleus containing a large 

 nucleolus lies in the distal half of the cell. The cells also contain 

 many small, scattered vacuoles and many spherical granules, .the 

 latter mostly in the proximal half. The chloragogue granules are 

 of different sizes and of a blackish brown colour in life ; they do 

 not stain with eosin. 



4. Nephridia. 



The nephridia of this species were well described by Hatai. 



They are present in 

 segments VII — IX in- 

 clusive, and in all the 

 segments behind the 

 twelfth to near the hind 

 end. The funnel lies 

 close to the ventral 

 blood-vessel on either 

 side of the body and is 

 of the same structure 

 as in Monopylephorus 

 trichochœtus Ditlevsen. 

 The main mass is a 

 more or less irregularly 

 elongated lobe lying by 

 the side of, and spread - 



Fig. 12. 

 Nephridia and related portions of the body ; 

 reconstructed from horizontal sections, x 100. bw — 

 body wall, ns — funnel, vv — ventral blood-vessel, np — 

 nephridiopore, nm — nephridia] main mass, sb — seta- 

 bundle, pt — ordinary peritoneal cells. 



