A Segmented Worm — Earthworm 391 



-b 



wall and filling the typhlosole may act to eliminate wastes. Solids are 

 eliminated through the anus. 



Coordination and Sensory Equipment. — A bilobed brain (supra- 

 pharyngeal ganglion) is located dorsal to the pharynx near segment III. 

 The circumpharyngeal ring or commissure encircles the pharynx and 

 connects the brain with the subpharyngeal ganglion below the pharynx. 

 The ventral nerve cord extends posteriorly from the subpharyngeal gan- 

 glion and has an enlarged ganglion (gang' li on) (Gr. ganglion, little 

 tumor) which gives origin to three pairs of nerves in each segment. 

 These ganglia serve as subordinate ''brains" where nerve impulses may 

 be received and redirected. Nerves connect the various body segments 

 to coordinate their various activities. The muscles of the setae are con- 

 trolled in order to make them perform their functions properly. 



There are epidermal sense organs in the peripheral tissues which when 

 stimulated send impulses over nerves. Sensory hairs penetrate the cuticle 

 and are connected with the nervous system. Earthworms react to light, 

 contact, moisture, chemicals, sound, etc. 



Reproduction. — Both male and female sex organs are present in the 

 same earthworm; hence, it is monecious (hermaphroditic ) . The female 

 organs include one pair of small ovaries (segment XIII) not visible from 

 the dorsal side, one pair of small oviducts which are modified nephridia 

 (segment XIII), one pair of egg sacs connected with the oviducts (seg- 

 ment XIV), one pair of oviduct openings on the ventral side (segment 

 XIV), two pairs of seminal receptacles (spermatheca) in segments IX 

 and X, and two pairs of seminal receptacle openings between segments 

 IX and X and X and XI. The male organs include two pairs of hand- 

 shaped testes (segments X-XI) covered by the seminal vesicles and not 

 visible from the dorsal surface, one pair of vasa deferentia (sperm ducts) 

 with ciliated funnels (segments X to XV), one pair of vasa deferentia 

 openings on the ventral surface (segment XV), and three pairs of large, 

 conspicuous seminal vesicles (segments IX to XII). The bases of these 

 vesicles are attached in these segments, although they may extend beyond 

 them. 



During copulation the ventral surfaces of two earthworms are in con- 

 tact, with the anterior ends pointing in opposite directions. A slimy, 

 bandlike cocoon (kokoon') (Fr. cocon, cocoon) secreted by the clitellum 

 encircles the two worms. A pair of temporary seminal channels is formed 

 on the ventral surface of each worm, so that sperm expelled from the 

 vasa deferentia of one worm travel to the openings of the seminal recep- 

 tacles of the other, within which the sperms are stored. Copulation 



