EARTHWORM. 



189 



therefrom ; they lie near the nerve-cord, attached to the 

 posterior surfaces of the septa between segments 9-10 and 

 io-ii. They are minute, translucent, and difficult to see. 

 In immature worms they lie exposed in the body cavity ; in 

 mature worms they are concealed by the great development 

 of— 



(2) The seminal vesicles, which are much-lobed struc- 

 tures, exceedingly prominent in dissection. Small and 

 laterally placed in young worms, in the adult the anterior 

 two pairs fuse in the middle line and cover the anterior 



5 



R.S 



ovd — pi 



Fig. 83. — Reproductive organs ot earthworm. 

 — After Hering. 



N., Nerve cord; T., anterior testes; S., sacs of setae; U.S., 

 receptacula seminis ; s., seminal funnels; v.o._, vas deferens; 

 ovd., oviduct; 011., ovary; s.v., seminal vesicles cut open; 

 VI II. -XV., segments. 



pair of testes and its ducts, while the posterior pair similarly 

 conceals the second pair of testes with its ducts. Into the 

 seminal vesicles mother-sperm-cells from the testes pass, 

 and there divide up to form spermatozoa. 



Development shows that the seminal vesicles arise as 

 outgrowths of the septa of segments 9-12, and that their 

 lumen is a portion of the body cavity. This is of importance, 

 for in Polychsetes the genital products mature in the general 

 body cavity, just as the spermatozoa in the earthworm 

 mature in the seminal vesicles. 



(3) From the seminal vesicles the spermatozoa are carried 



