22 



E. NOMUP.A : 



Fig. 17. 



Cross section of longi- 

 tudinal heart, x 400. mf— 

 circular muscle fibre, cf — 

 contractile fibrils, pt — cel- 

 lular peritoneum, ic — dor- 

 sal intestinal vessel, n — 

 ? nerve cell, in — intima. 



In each segment behind the third, the dorsal vessel swells 

 more or loss just in front of the posterior septum, where it is 



provided with a group of valvular cells. These 

 cells are large and somewhat ovoidal in shape, 

 and the thin finely granular cytoplasm does 

 not stain with eosin in contrast to the blood 

 which stains very deep ; the nuclei are very 

 small and spherical and lie in the middle of 

 the cell. 



The wall of the pulsatory lu-art is thick 

 compared with that of the ordinary vessels 

 and consists apparently of three layers (fig. 

 17). The outermost layer is that of the cel- 

 lular peritoneum, which is followed by a layer 

 of contractile fibrils of the same structure as 

 the ' curious layer ' described in my previous 

 paper on Limnodrilus gotoi ; tins layer 

 is sometimes interrupted by cells which 

 may possibly be nervous in nature. 

 Inside this there lies a comparatively 

 well developed, circular muscle layer, 

 invested internally by a thin intima. 

 2). The ventral vessel runs through 

 the whole body length along the 

 ventral median line on the dorsal side 

 of the nerve cord, independently of 

 the alimentary canal. The calibre of 

 the ventral vessel is always smaller 

 than that of the dorsal and no valves 

 are attached to its inner wall. In the anterior part of the vessel 

 are found here and there many blood corpuscles (fig. 18), ellip- 



v.l.v 



Fig. 18. 



Cross section of ventral vessel 

 passing through the origin of the 

 anterior ventral integumentary 

 vessels, x 400. pt — cellular peri- 

 toneum, mf — circular muscle fibre, 

 v.l.v — ventral integumentary A r essel, 

 b.c — blood corpuscle. 



