632 



In transverse section it is ovoid in shape. Studies on the living speci- 

 mens revealed the fact that the depth of the posterior emargination 

 is subject to some variation, depending upon certain changes in the 

 states of contraction of the animal. Sometimes the emargination is 

 rather shallow, although always distinct ; at other times the emargina- 

 tion is deep. Two pairs of strands connect the brain with the body 

 wall, one pair arising from the lateral margins of the brain and 

 the other pair from the posterior lobes. 



Blood Vascular System. — Studies of both living and preserved 

 specimens show that the dorsal vessel arises in XIII. A distinct 

 swelling of this vessel occurs in XIII, where the diameter exceeds 

 that of any other region. No cardiac body is present. The peri- 

 visceral sinus appears in the region of the clitellum, and in transverse 

 sections of the worm has a distinctly beaded appearance entirely 

 around the intestine. There is reason to believe that this appearance 

 is due to the fact that there are membranous partitions which run 

 lengthwise of the sinus, thus dividing it into a number of longitudi- 

 nal tul>es. These tubes appear to be distended with blood, and when 

 sectioned transversely exhibit a more or less circular outline. This 

 sinus extends posteriorly from the origin of the dorsal vessel, and 

 shows a decided reduction at the septa. The ventral vessel branches 

 at IV/V. The blood is yellowish in the living specimens. 



Ncphridia. — The first nephridia are connected with VII/VIII. 

 The anteseptal part (PI. CII, Fig. 33) is very small and consists merely 

 of the nephrostome. The postseptal part is large, elongated pos- 

 teriorly, and flattened laterally. The efferent duct arises from the 

 ventral side of the postseptal part, slightly anterior to its posterior 

 end. 



Spcrniidiical Fuiuicl. — The spermiducal funnel is about twice as 

 long as its average diameter. In some specimens the funnel is slightly 

 flattened laterally. A set of typical measurements are as follows : 

 length 0.07 mm ; average diameter 0.039 mm. The duct is very long, 

 much contorted, and confined to XII. 



Penial Bulb. — This organ is well developed, and is rather con- 

 spicuous in transverse sections. It is situated on a distinct invagina- 

 tion of the body wall. It is globular in shape (PI. CII, Fig 34), partic- 

 ularly in cases where it is extruded. In the retracted condition it 

 is ovoid. The organ as a whole is covered with a thin peritoneal 

 layer, beneath which lies a comparatively thin layer of muscle tis- 

 sue. The body of the bulb is composed of a large number of similar, 

 more or less spindle-shaped cells, whose long axes extend towards 

 the external surface. Each cell is conspicuously nucleated and usu- 



