254 FEANK E. BEDDARD. 



The spermathecal orifice was not visible upon the 

 exterior; by means of transverse sections it was found to be 

 upon Segment 11. 



The most characteristic external mark of this species is 

 afforded by a series of sucker-like structures. There are 

 six of these, one to each of Segments 10 — 15. The last three 

 are accurately median and ventral in position, and are situated 

 on about the middle of their segment. The two in front are 

 placed considerably to the left of the middle line, as shown in 

 fig. 21 ; the first is nearer to the middle line. 



§ Integument. 



The epidermis of Heliodrilus agrees in every particular 

 with that of Hy period ril us, as does also the structure of 

 the clitellum. The limits of this modified region of the 

 body-wall could not be ascertained with certainty by an inspec- 

 tion of the worm ; transverse sections show that it extends over 

 Segments 14 — 17. 



The peculiar sensory organs which are so characteristic of 

 the Eudrilidse occur in Heliodrilus; their structure calls for 

 no remark, as they resemble in every particular those of 

 Hyperiodrilus, which have been already described on p. 236. 



The muscular layers of the integument are also identical in 

 every respect with those of Hyperiodrilus. 



§ Alimentary Tract. 



The buccal cavity occupies the first three segments. 



The pharynx extends back to the 6th segment. 



The oesophagusis very narrow, and passes back without any 

 change as far as the 10th segment ; here it becomes narrower, 

 and the lining epithelium is thrown into a series of regular 

 longitudinal rugae; at the mesentery before the 11th segment, 

 as in the case of the subsequent segments, it becomes a trifle 

 wider, recurring to its former dimensions, which are between 

 one third and one fourth of the diameter of the body of the 

 worm in this region. The first of the two ventral oesophageal 

 pouches lies in this segment, and is directed forwards, having 

 anteriorly no connection with the wall of the oesophagus; 



