LUMBRICUS TERRESTRIS I75 



the testes, is a pair of large ciliated funnels with folded walls, 

 known as sperm rosettes. These funnels lead into the vasa effer- 

 entia, of which the two on each side join and pass back as a vas 

 deferens to open on somite 15. The cilia of the rosettes draw the 

 ripe sperm into the ducts. 



Copulation (Fig. 109) takes place at any time from spring to 

 autumn in warm, damp weather, with a maximum frequency in 

 the hot weather of summer. Two worms stretch themselves out 

 of their burrows and place their ventral sides together with the 

 heads pointing in opposite directions, their bodies being held 

 together by a substance secreted from the clitella, and by the 

 chaetae, which stab into the body-wall of the partner. They remain 

 like this for two or three hours, and sperms are passed from the 

 vas deferens of each worm, along a temporary seminal groove, 

 into the spermathecae of the other. Some time after the worms 

 have separated the eggs are laid in a cocoon, which, secreted by 

 the clitellum as a broad band round the body, is passed forwards 

 over the head. The cocoon contains a nutrient fluid. While it is 

 still on the clitellum eggs are passed back to it along a temporary 

 groove from the oviducal opening, and as it passes the sperm a- 

 thecal openings, semen received from another worm is squeezed 

 into it and fertilisation takes place immediately. In passing over 

 the head the ends of the elastic cocoon close, and it becomes a 

 small, lemon-shaped body, which is left in the earth. Each cocoon 

 contains eight to sixteen ova, which are fertilised in it, but usually 

 only one completes development, a process which takes several 

 weeks. The development of the earthworm is referred to on p. 670. 



REGENERATION 



Many earthworms have an extensive power of regeneration, 

 which depends on a hormone secreted by the central nervous 

 system. If the body be cut in half, the head end will grow a new 

 tail, and the tail end, though more slowly, a new head. It appears 

 that, of the two common species described above, Allolohophora 

 chlorotica does regenerate, but Litmbriciis terrestris does not. 



NEREIS CULTRIFERA 



The earthworm has a burrowing habit and a vegetarian diet. 

 Many marine worms, however, while they resemble the earthworm 



