THE EARTHWORM 



209 



out the transferred impulse, the muscles will contract, and 

 the animal moves away. This kind of nerve-action is called 

 reflex action because, in a sense, the impulse is reflected back 

 from the ventral nerve-chain. 

 Reproduction. Every earth- 

 worm contains both spermaries 

 and ovaries. As explained on 

 page 176, animals which have 

 the male and female glands in 

 the same body are called her- 

 maphrodites. There are two 

 pairs of spermaries in the earth- 

 worm hidden by the three pairs 

 of seminal vesicles^indic'dted in 

 Fig. 100, 30, 31. The single pair 

 of ovaries (Fig. 100, 35) is very 

 small. Although each earth- 

 worm produces spermatozoa 

 and eggs, the eggs of one indi- 

 vidual are always fertilized by 

 the spermatozoa of another. 

 During the breeding season, 

 which extends through the 

 greater part of the year, earth- 

 worms occasionally meet be- 

 neath stones and logs, and affix 

 the ventral surfaces of their 

 bodies together by the anterior 

 thirds pointed in opposite directions, and each expels a quan- 

 tity of its spermatozoa which, are received in cavities of the 

 other, opening from the outside. These cavities (seminal 

 receptacles) are four in number, and are in the ninth and tenth 

 somites (Fig. 100, 33, 34). They retain the spermatozoa until 

 the eggs are ready to be laid. 



FIG. 102. Reflex Action in the Earth- 

 worm. (Reconstructed from 

 drawings by Havet) 



(The arrows indicate the path of the ner- 

 vous impulse) 



1, cuticle of skin ; 2, sensory nerve- 

 ganglion ; .'$, sensory nerve-fiber ; 

 4, anterior branch of sensory nerve- 

 fiber ; 5, posterior branch of sensory 

 nerve-fiber ; 6, ventral nerve-cord ; 

 7, motor nerve-ganglion ; 8, motor 

 nerve-fiber; 9, longitudinal muscle- 

 fibers 



