AND ZOOGEOGRAPHY OF IXDIAjSF OLIGOCH.'ETA. 



133 



VI. — On the Relationships of the Genera of Moniligastrid^e ; 

 WITH some Considerations on the Origin of Terrestrial 



OlIGOCH.'ETA. 



(1) The Testis Sacs of the Oligochceta. ■ 



The primitive condition of the male organs of the Oligochseta 

 is that seen in most of the lower families as well as in many 

 Megascolecidfe and Lnmbricidse. The testes are attached to the 

 anterior wall of their segment,, the funnels to the posterior ; the 

 sperm cells are shed into the C(jelomic cavity at an early stage of 

 their development, and ripen in the general cavity of the 

 segment, or more usually in csecal sacs, the seminal vesicles, 

 formed by bulgings of the septa (text-fig. 7). In this case there 

 are no testis sacs. 



Text-fifi-ure 7. 



Primitive condition ; no testis sacs, f., male funnel ; s.v., seminal vesicle 

 (shown in-segms. ix and xii) ; t., testis ; o.d., vas deferens. 



Not infrequently, however, it happens that the lower part of 

 the segment, where the testes and' funnels lie, is cut off by a 

 partition from the rest of the cavity of the segment. The 



Text-figure 8. 



The ordinary form of testis sacs, e. g. as in Lumbricus. References as before ; 

 in addition, t.sac, testis sac (median seminal vesicle). 



organs are then contained in special compartments of the ccelom, 

 the testis sacs— either a single one in each testicular segment, 



