SEA-FISHERIES LABORATORY. 319 



and a peritoneal covering 1 . The muscle layer is only 

 feebly developed in worms of this size, it becomes much 

 more highly developed in older specimens (see figs. 33, 40). 

 The protoplasm of the peritoneal cells is moderately homo- 

 geneous, in older stages it becomes either vacuolated or 

 granular and in many cases contains chlorogogen granules. 

 The wall of the heart is invaginated forming a club-shaped 

 process which contains a central cavity- The very thin 

 endothelium is only partly shown, being obscured in the 

 rest of the preparation by a mass of blood. (Cf. figs. 33, 

 40). x 600. 



Fig. 39. Longitudinal section of the thicker-walled 

 muscular ventricle of a large specimen 250 mm. long. 

 The invaginations of the wall are very numerous and 

 complex, filling up the greater part of the cavity and 

 forming the well-marked heart body. x 45. 



Fig. 40. The tip of one of the invaginated processes 

 of the heart-body, from the previous figure, showing the 

 endothelium, the muscle fibres and the core of loosely 

 arranged peritoneal cells, some of which are vacuolated 

 and some granular. x 260. 



Fig. 41. Three blood corpuscles. The one on the 

 right from an old specimen (250 mm. long), the two others 

 from a young specimen (65 mm. long). x 1000. 



Fig. 42. The terminal portion of one of the small 

 cpecal branches of the ventral vessel covered with irregular 

 dark brown chlorogogen cells. The latter do not extend 

 to the tip of the vessel. x 150. 



Fig. 43. Section of the covering of the ventral vessel, 

 the columnar cells loaded with yellowish chlorogogen 

 granules of various sizes. x 500. 



Fig. 44. Coelomie cells. In the upper part of the 

 figure a typical fusiform cell, on the right four amoeboid 

 cells, three of which contain chlorogogen granules ; on the 



