ON MONOPYLEPHORUS LIMOSUS. 



31 



25, at), which is spindle-shaped and longer than half the segment 

 length. Its anterior half, to which fibres of the parieto-visceral 

 muscle are attached, lies near and on either side of the ventral 

 nerve cord, while the posterior half is more removed from the 

 vertical median plane of the body and lie in the dorso -lateral part. 

 The widest part of the organ lies at its middle and is 3-4 times 

 the diameter of the vas deferens. It is almost squarish or circular 

 in cross section and shows folds on its inner surface. The wall of 

 the atrium consists of three layers, an inner of ciliated tall columnar 

 cells, similar to those of the vas deferens, a thin middle layer of 

 muscle fibres, and an outer thick layer of pear-shaped gland cells 

 with dense granulated cytoplasm and a large nucleolated nucleus 

 at the distal part. From the proximal narrow end of each gland 



ps 



*J m 4—* ' « » * >■ . '"Sfc 4 *-*" 



dp- 



—1.1 



Fig. 26. 



Cross Sectio q through the male pore of a protandrously mature specimen, x 150. 

 Cœlomic corpuscles are not shown, ps-^posterior sperm-sac, d.v — dorsal vessel, dp — atrial 

 duct-portion, 1.1 — lateral line, i n — intestinal vascular network, v.v — ventral vessel, tb — 

 transversal bridge, mp — median male pore, nc — ventral nerve cord. 



