134 



DR. J, STEPHENSON ON THE MORPHOLOGY, CLASSIFICATION, 



containing the organs of both sides, or a pair in each segment, 

 one for the organs of the i-ight and one for those of the left side. 

 Thus in the common European genus Lumhricus there is a single 

 testis sac (often called the median seminal vesicle) in each of the 

 testis segments ; while in many species of the common Indian 

 genera, Pheretima and Eutyjyhmus, the sacs are paired (text- 

 tig. 8). 



In the genus Ocnerodrilus, and in a few species of Enchytrceus, 

 testis sacs of a different type are found. The sacs enclose the 

 testis, and are a,ttached like the latter to the anterior septum of 

 the segment, projecting freely into its cavit}- ; the funnels, 

 however, are outside the sac, and, as usual, on the posterior 

 septum of the segment ; it is evident that the sac must rupture 

 before the spermatozoa can enter the funnel. In this case the 

 sac can hardly be anything else than the superficial layer of the 

 proliferating peritoneal cells which give rise to the gonad ; this 

 layer separates off as a connected membrane, beneath which the 

 genital cells are shed and ripen (text-fig. 9) *. The lobes of the 



Text-figure 9. 



tsacf t 



I'd. 



Testis sacs of Ocnerodrihis oceidentalis. References as before. 



testes of some species of Luinhricillus are also (at any rate in 

 their young state) surrounded by a thin membrane, within 

 which the genital cells are cast off and undergo some of tlieir 

 development. 



Lastly, in all the Moniligastridae the testis sacs are paired 

 vesicles, suspended by the septa in such a way that they project 

 into the segment in front or into the segment behind, or (more 

 xisually) into both; the degree of projection forwaids or 

 backwards varies in different individuals of the same species, 

 and sometimes on the two sides of the same individual. Within 

 each sac — usually perhaps on its floor towards the anterior wall — 

 is the testis, a proliferation of the epithelial lining of the sac ; 

 the funnel is also included in the sac, and is situated on the 



* I do not know of ai\y observations on migration of genital cells in tlie Oligo- 

 clircta. If sucli took place, it might be possible to interpret the sac wall in these . 

 cases as the peritoneum, raised np and distended by the ripening germ cells which 

 had taken np their position beneath it. 



