THE NEPHRIDTA OP THE POLYOH^TA. 733 



running together of their lips, the functional meaning of 

 which is not clearly understood. There is little difficulty in 

 supposing that it has been independently acquired, and is 

 peculiar to the family. 



The exact mode of origin of the connection between the 

 nephrostome and the genital funnel in the third group is 

 more difficult to determine. It might conceivably have come 

 about, as indicated above for the Phyllodocidse, by a gradual 

 approximation of two originally distinct apertures, and the 

 subsequent shifting of the genital funnel on to the tip of the 

 nephridium ; or, as in the Capitellidge, by the fusion of the 

 lips of the two organs, followed by the loss of the primitive 

 genital pore. On the whole, I am inclined to think that 

 neither of these processes was the one adopted in this case ; 

 but that the connection took place owing to the nephrostome 

 itself becoming so closely situated to the end of the genital 

 funnel, as the latter grew towards the epidermis at maturity, 

 that a fusion took place, leading to the grafting of the 

 genital funnel on to the internal extremity of the nephridium.^ 

 The genital products then passed down the nephridial canal, 

 instead of directly to the exterior. It will be noticed that 

 the nephrostome of the Hesionidte is situated very close to 

 the body-wall. This interpretation seems to be supported by 

 Meyer's description of the development of the excretory 

 organs of Polymnia (22), where the inner end of the ne- 

 phridial rudiment is represented as fusing with the apex of 

 the developing funnel. 



Judging by the very similar final results obtained, it is 

 from some such mode of union as this which has been de- 

 monstrated in the Hesionidoe, that the compound large- 

 funnelled excretory organs of the majority of Polycheetes 

 (Syllids, Eunicids, Aphroditids, Amphinomids, etc.) have 

 been formed. 



The consideration of the structure and homology of the 



' Tbe usefulness of the ciliated genital funnel in accumulating waste pro- 

 ducts in the neighbourhood of the nephridium has, no doubt, in all three 

 cases contributed to bring about the " rapprochement." 



VOL. 43, PART 4. — NEW SERIES. E E E 



