aS Game 
239 
of three layers, an endothelium internally, a muscle layer 
and a peritoneal covering. ‘The muscle layer is only 
feebly developed in worms of this size, it becomes much 
more highly developed in older specimens (see figs. 35, 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 excessively 
thin endothelium is partly obscured by a mass of blood 
which closely invests the process. (Cf. figs. 33, 40). x 600. 
Fig. 59. Longitudinal section of the much thicker, 
muscular ventricle of a large specimen 250mm. 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 46. 
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 1260) 
Fico. 41. Three blood corpuscles. The one on the 
g | 
right from an old specimen (250 mm. long), the two others 
from a young specimen (65 mm. long). x LOOO. 
Fig. 42. The terminal portion of one of the small 
execal 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. 
ig. 48. Section of the covering of the ventral vessel, 
the columnar cells loaded with yellowish chlorogogen 
granules of various sizes. x 500. 
Fig. 44. Coelomiec cells. In the upper part of the 
figure a typical fusiform cell, on the mght four ameeboid 
cells, three of which contain chlorogogen granules; on the 
