466 



ANNELIDA. 



pairs of the anterior nephridia become much enlarged as renal organs, 

 while the nephridia of the posterior part of the body become much 

 reduced, and serve as genital ducts. 



Reproductive organs. The Polychaets are mostly dioecious, but 

 a few are hermaphrodite (some Sabelliformia, e.g., AuipMglena, 



nepti.p. 



FIG. 370. Nephridium of Nereis (after Goodrich, diagrammatic). The nephridial tube opens 

 internally at neph.fun., externally at nepli.p., and is divided into four regions; p. s. can. 

 postseptal canal. 



Salmacina, Protula, Spirorbis, and some Hesionidae). The gonads, 

 which are differentiations of the coelomic epithelium, are not so 

 narrowly localized as in OUgochaeta, but are more diffused over the 

 body on the walls of blood vessels, on the intestinal wall, or even 

 on the body-wall.* The products, when ripe, are dehisced into the 



k. 



FIG. 371. Nephridium of Arenicola marina (after Vogt and Yung). vesicle ; b glandular 

 appendage ; c funnel ; d lower, e upper lip of funnel ; / opening of funnel into the vesicle ; 

 g nerve cord ; h longitudinal muscles ; i line of insertion of setae ; k setigerous sacs ; 

 I aggregation of reproductive cells. 



* Cosmovici, Arch. Zool. Expcr., 8, 1879-80. 



