290 PROCEEDINGS OF THE NATIONAL MUSEUM vol. ii4 



longer structure capable of being itself everted independently of the 

 bursa. The evolutionary trend in this particular is obvious enough. 



In Cambarincola, the penis is invariably of the short cone type, 

 and does not, in repose, extend ectad beyond the major band of 

 cu'cular muscle which approximately divides the bursa into halves. 

 Dui-ing copulation it is carried to the exterior by eversion of the 

 bursa, which thrusts the penis and associated penial sheath down 

 through the atrium and to the position it occupies as a median projec- 

 tion in a circular, distally concave structure formed by the lining of 

 the atrium. This displacement of the atrium dm"ing eversion can be 

 appreciated by comparison of the guide letters a through d in figures 3 

 and 4, showing that the inner wall of the atrium becomes the outer 

 surface of the everted bm"sa. As the penis is, in this genus, capable 

 of only limited penetration of the spermatheca of the copulatory 

 partner, it is evident that the animals are obliged to achieve and 

 maintain a very close ventral contact dm-ing the process of sperm 

 transfer. 



Eversion of the bursa is accomplished partly by contraction of 

 the circular muscles of the ental half, and doubtless also in part by 

 internal pressure achieved by contraction of the segmental muscles. 



Summary of the male sex organs. Holt (1949) has shown that 

 the entke male system, with the exception of the funnels and possibly 

 the efferent ducts, is ensheathed by peritoneum, and all of the organs 

 so invested are probably derived from the body wall. The interested 

 student is referred to this paper for a more detailed treatment of the 

 reproductive system. For the present, I consider them chiefly from 

 the standpoint of then- taxonomic utility. 



It is postulated that the primitive arrangement for the family 

 consists of two pairs of testes, funnels, and efferent ducts, one pair 

 each in segments v and vi; two deferent ducts which merge into a 

 Y-shaped glandular enlargement, the spermiducal gland — which 

 probably lacks a prostate, and which does not extend entally beyond 

 the entry of the deferent ducts; a thin-walled, muscular ejaculatory 

 duct, and a simple, fusiform, eversible bm-sa which carries a short, 

 conical, unmodified penis in its ental half. 



Except for the presence of a prostate, the animal which comes 

 closest to answering this description is a species of Cambarincola, to 

 be described in a following section. Species which are almost anti- 

 thetical to the foregoing are likewise known, but are members of 

 North American genera as yet undescribed. However, a general 

 progression away from most of the stipulated conditions can be found 

 within the confines of the genus Camharincola, suggesting its status 

 as a dynamically evolving genus which has nonetheless retained, in 



