358 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



development of the sperm-sac, there is little difficulty in 

 understanding this. The sperm-sac extends forwards into 

 segment 9, and backwards as far as segment 16, in both 

 cases ending blindly. There remains, however, an 

 opening from the sperm-sac into segment 10, from which 

 it was derived as simple, pouch-like outgrowths of the 

 anterior and posterior septa, respectively. Although the 

 structure of the sperm-sac becomes much more com- 

 plicated as the worm matures, the sac retains its 

 connection with segment 10, and so the spermatozoa can 

 pass into the coelom, and thence to the surface of the 

 expanded funnel of the vas deferens which lies in the 

 same segment. 



IV. The Sperm Ducts or Vasa Deperentia. 



The spermatozoa when mature are conveyed to the 

 exterior by special ducts known as the sperm ducts or 

 vasa deferentia. As is always the case in the Oligochaeta, 

 the number of these ducts corresponds to the number of 

 the testes, therefore in Tubifex rivulorum there is a 

 single pair. Each duct consists of a much coiled tube 

 with its origin in segment 10 — the segment which 

 contains the testes; and its external aperture in 

 segment 11. The whole duct, however, does not lie in 

 these two segments — its length is so great and it exhibits 

 such complex coiling that it extends posteriorly through 

 several segments, sometimes reaching as far back as 

 segment 15. 



For the purpose of description we can divide the sperm : 

 duct into the following regions: — (1) The ciliated funnel 

 (PI. I, fig. 2, ci.f.), (2) the coiled tube (PL I, fig. 2, 

 v.d. 1, v.d. 2), (3) the spermiducal gland with the prostate 

 (PI. I, &g. 2, at.), and (4) the penis (PI. I, fig. 2, pe.). 



