480 



ZOOLOaY; 



SEOT, 



be prolonged for some distance in the interior of the nephridium 

 itself The resemblance between those solenocytes and the 

 flame-cells of Platyhelminthes will at once be recognised. 



In the Polychseta another set of segmentally repeated structures 

 are frequently intimately connected with the nephridia. These 

 are a series of pairs of ciliated funnels, the ccelomoduds, opening 

 widely into the cuelome, and, in a typical case, communicating with 



Fkj. y77. — LHagram to illubtratc the variuuy curiibiuatiuns of closed and open nepbridia and 

 coclomoducts in the Folycha^ta. 



I". HypoUietieal stage with closed nephridia and separate ctBlomoducts ; b, condition in 

 which the cujlonioducts have become united with the nephridia ; this occurs in Pkyilo- 

 docidcc and GoniaiUdxe ; c, condition in which the coalomoduct becomes reduced to a ciliated 

 organ (^NcphtkyiOxn) ; Ila, combination of nephridia with nephrostomes and separate ccelonio- 

 ducts iDasybyanchvff) \ 0, condition in which " segmental organs " are formed by the union 

 of nephridia with nephrostomes and ciMloraoducts (the most usual condition) ; r, condition in 

 which there are nephridia with nephrostomes, and the e(«lomoduets are reduced to ciliated 

 organfi(Nf-i-eis, etc.). The nephridia are outlined with a thick line : the ccelomoducts striated. 

 (After Goodrich.) 



the exterior. In Nereis they are represented by the dorsal ciliated 

 organ, and arc not known to open externally. When provided 

 with external apertures, as is usually the case, the coelomoducts 

 act as the efferent ducts for the sexual elements. In many of the 

 Polychreta they do not remain independent, but coalesce partially 

 or completely with the nephridia, and the functions of excretory 

 organs and reproductive ducts become combined in the one set of 

 " segmental organs " (Fig. 377). In some families of Polychteta 



