296 CALIFORNIA ACADEMY OF SCIENCES. 



and it is probably this which causes the body to bend. 

 The upper part of the clitellum is much thickened and of 

 the same general structure as in Ocnerodrilus. The 

 lower part of the clitellum is gradually thinned out to- 

 ward the genital zone, below which and the ventral line 

 the body-wall is not differentiated. 



Genital zone (figs. 3 and 23). As has been already 

 stated the male pore as well as the prostate pores open 

 on an elevated zone not unlike that one described by 

 Beddard in Gordiodrilus, only the zone is paired, there 

 being one on either side of the median line. Between the 

 two zones there is a cylindrical cavity of even width run- 

 ning exactly below the ventral ganglion and across 

 somites xvii, xviii and xix. There are no papillae in this 

 cavity, nor is there any connection between it and the 

 genital zone. But in each of the three somites, covered 

 by the cavity, there is a transversal muscle which 

 stretches across it and which contracts the body in such 

 a way as tobring the genital zones closer together, which 

 again gives rise to the tubular cavity. The genital zone 

 on either side is crescent-shaped, the convex part of the 

 crescent being toward the ventral median line of the body, 

 that is, the points of the crescent are turned away from the 

 ventral ganglion. The anterior and prosterior part of 

 the zone ends each in an oblong papilla thicker at the 

 point furthest away from the ventral nerve ganglion. 

 The center of the convex side of the crescent is fur- 

 nished with a large oblong papilla, which does not extend 

 across the crescent to its concave side. In the center of 

 this papilla on the margin of the crescent is situated the 

 pore of the sperm duct. In the anterior papilla opens 

 the pore of the anterior prostate, while in the posterior 

 papilla opens the posterior prostate. In the center 

 of the genital zone is a semicrescent-shaped depression. 



