112 



ANNELIDA OR ANNULATA 



Male 



Paired testes in the loth and nth so- 

 mites. 



Three pairs of seminal vesicles at- Paired vasa deferentia opening at the 

 tached from the 9th to the 12th 15th somite, 

 somite. The last pair, bi-lobed, 

 extend down over the 13th and 

 sometimes the 14th somite. 



\ PJl 



MR 



Fig. 48. Nervous system of the earthworm. Drawing showing a lateral view 

 of the arrangement of the larger nerve trunks in the left half of the anterior segments 

 of the earthworm, Lumbricus terrestris. A, nerve from lateral region of cerebral 

 ganglion which passes to prostomium; AN, dorsal ramus of anterior segmental nerve; 

 AR, ventral ramus of anterior segmental nerve; 5, nerve from near middle region of 

 circumpharyngeal connective which passes to segment i; 5C, buccal cavity; C, nerves 

 from ventral region of circumpharyngeal connective which pass to segment 2; CG, 

 cerebral ganglion; CPC, circumpharyngeal connective; D, branch of nerve to pro- 

 stomium that supplies tissues of dorsal region of buccal cavity; £, nerve that supplies 

 the portion of the prostomium in the dorsomedian region of segment i; F, gangliated 

 thickening of enteric nerve plexus; G, branch of nerve to segment i that supplies 

 tissues of ventral region of buccal cavity; L, septal nerve; M, mouth opening; MTV, 

 dorsal ramus of median segmental nerve; MR, ventral ramus of median segmental 

 nerve; P, prostomium; PN, dorsal ramus of posterior segmental nerve; PR, ventral 

 ramus of posterior segmental nerve; SG, subpharyngeal ganglion; I-VI, segments i to 6. 

 (Courtesy of W. N. Hess, Journal oj Experimental Zoology, vol. 40, p. 235.) 



Conjugation. — Two earthworms pair so that segments 9, 10 and 

 II of each animal are opposite the clitellum at segments 31-37, and 

 the vasa deferentia of each animal are nearly opposite the 26th seg- 

 ment of the other where the setigerous glands are modified. Mucus 

 secreted by the clitellar and other glands of each worm becomes 

 hardened into a single " slime-tube " encasing both animals from the 



