SPECIES OF THE GENUS AULODRILUS. 



949 



lateral line are small, about 15 by 6-9 /x in size, have an irregular 

 form and contain a corispicuous rounded nucleus of 4 ju diameter ; 

 they are only 4-5 in number in each transverse section. 



The clitellum extends over segments 7 and 8, which contain the 

 principal geuital organs; it leaves free the area on the ventral 

 surface occupied by the spermiducal chamber (PI. I. fig. 4). It 

 is opaque white in appearance and merges gradually into^ the 

 epidermis in front and behind. Its cells are about 70 /^ in height, 

 ^. e., about four times as high as the ordinary epidermal cells. In 

 the clitellar cells the cell outlines are lost, and the nuclei dis- 

 appear, though these may be visible in the early condition lying 

 here and there near the inner border. The cells have a coarse 

 granular appearance; the mucous gland cells are present in the 

 clitellum also. 



Text-fig. 2 B. 



al.pe.s.s. /.t-\ 



Vertical sections through the penial setal sac and the glandular masses in con- 

 nection with it in two diflerent specimens. The penial seta is rooted in the 

 wall of the setal sac. X 390. 



[For explanation of letters used in the figures, see p. 969.] 



Setal Sacs. — In the sexual phase the ventral setal sac of 

 segment 7, which contains the penial setse, is nearly circular in 

 outline as seen in a transverse section of the body (PL I. 

 fig. 2). Its wall consists of tall columnar epithelial cells of 

 about 18 by 2"5 /x size, containing a few nuclei near the outer 

 periphery ; outside the epithelium there is a thin layer of muscle 

 fibres. Cell outlines are not recognizable in the greater portion 

 of the penial setal sac, except for a small portion on its A'entral 

 surface, on account of the secretion, with which the cells seem 

 to be filled ; the nuclei are also mostly lost in this region 

 (text-fig. 3), though they are easily recognized in the ventral 

 portion of the wall, where the secretion is not present. The 



Proc. ZooL. See— 1922, No. LXIY. 64 



