118 



Write an Account of the Reproductive System of Lumbricus. 



The Earthworm is hermaphrodite. Under the alimentary 

 canal there are two median seminal vesicles (in segments 

 10 and 11). and, connected with these, three pairs of 

 lateral seminal vesicles. Inside each median seminal 

 vesicle, and attached to the septum in front of it, there 

 is a pair of small lobed testes. Beside each testis is the 

 funnel-shaped opening of a seminal duct. The two short 

 seminal ducts on each side pass through the posterior 

 septa of their respective segments and unite to form the 

 longer vas deferens ; the two vasa deferentia open on the 

 ventral surface of segment 15. The sperm-forming cells 

 pass from the testis into the seminal vesicles, and there 

 the active hair-like spermatozoa are formed. 



The female organs are two small pear-shaped ovaries, 

 attached by their broader ends to the septum between 

 segments 12 and 13, one on each side of the nerve cord. 

 Opposite them, on the septum behind, are the funnel-like 

 -openings of two very short oviducts which open to the 

 ^exterior on the ventral surface of segment 14. Two small 

 acs, the receptacula ovorum, open into the funnels of the 

 oviducts. The ripe eggs from the ovaries pass into the 

 ooelome, and thence down the oviducts. 



. When two worms unite (the head of one beside the tail 

 ; of the other) one of them acts as male; and the spermatozoa, 

 passed out from the vasa deferentia, are received by the 

 other worm into the spermathecae or receptacula seminis, 

 two pairs of globular pockets in segments 9 and 10. 



The worm casts off a membranous sheath secreted by 

 the clitellum (a thickening of the integument from the 

 -thirty-second to the thirty- seventh annulus inclusive). 

 This sheath is slipped off forwards ; passing over the 

 openings of the oviducts and spermathecae, it carries away 

 some eggs, and sperms are squeezed out. The ends of 

 the cast sheath close in, and thus an elastic cocoon is 

 formed containing eggs and sperms. Conjugation follows 

 ^(fertilisation is therefore external), and the development is 

 direct. 



