268 ELEMENTARY BIOLOGY. [CHAP. 



1. The reproductive organs. (Cf. Sect. C. e.) 



I. Obtain the body of a sexually immature worm (i.e. 

 one in which there is no trace of clitellum) which has 

 been well hardened in alcohol. Open up the an- 

 terior twenty segments along the dorsal middle line 

 and remove the alimentary canal with care, leaving 

 the mesenteric septa undisturbed. Look for — 



a. The sper7nathecce^ two pairs of small yellowish- 

 white globular bodies, attached to septa 9 — 10 

 and 10 — II. 



They are developed within the substance of the 

 septa referred to, and may project forwardly into 

 segments 9 and 10 or backwardly into 10 — 11. 



Their points of exit are invariable, and they may 

 conveniently be used as landmarks in dealing with 

 the remaining organs of the reproductive system. 



h. The se??iinal vesicles, three pairs of soft whitish organs 



attached — in the sexually immature worm — to septa 



9 — 10, 10 — II and II — 12. They are internal to^. 



In the sexually mature animal they unite with each 



other and their fellows of the opposite side, below 



the alimentary canal, so as to form two masses ; an 



anterior bilobed one on either side, the body of 



which lies in segment 10, and a posterior unilobed 



one for segment 11. 



c. Remove the seminal vesicles of one side and ex- 

 amine the mouths of the vasa deferentia {ciliated 

 rosettes). They are dead-white glairy structures, 

 lying near the middle line in segments 10 and 11 ; 

 when fully formed exceedingly conspicuous and 

 chalky looking. 



d. Trace back the ducts of c, on one side. Each per- 

 forates the septum behind it and becomes im- 



