2l8 



PHYLUM ANNELIDA. 



posterior surfaces of the septa between segments 9-10 and 

 lo-n. 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 the seminal vesicles. 



(2) The seminal vesicles are much-lobed structures, 

 exceedingly prominent in dissection. Small and laterally 

 placed in young worms, in the adult the anterior two 



f 



\XH 



Lvd 



^m 



xtv 



ov 



ovd 



FIG. 113, Reproductive organs of earthworm. 

 After Hering. 



JV., Nerve cord; 7 1 ., anterior testes ; S., sacs of setae; I\.S., 

 receptacula seminis ; s.f., seminal funnels; v.d. t vas deferens ; 

 ovd., oviduct; 0v., ovary; sv., seminal vesicles cut open; 

 VI1L-XV., segments. 



pairs fuse in the middle line and cover the anterior 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, 



