THE NEPHEIDIA OF THE POLYOflJlTA. 741 



From this table it will be seen that the Polychgeta fall into 

 two main groups : the first having closed ''protonephridia/' 

 the second provided with nephridia opening into the coelom. 

 This last may further be subdivided into those in which the 

 genital funnel retains its independent opening to the ex- 

 terior, and those in which this opening has been lost. The 

 latter may again be classed according to the extent of the 

 fusion between the funnel and the nephridium, which gra- 

 dually entirely loses its own nephrostome. 



I should not, of course, propose to base a new classification 

 on our present knowledge of these organs, and the table 

 must not be taken to represent an attempt at a phylogenetic 

 classification. Yet it is clear that these results must be 

 taken into consideration in reforming the classification of the 

 Polychseta. 



In conclusion it may be pointed out that, whereas in most 

 Annelids, and so far as we know in all other Coelomata, the 

 genital funnels remain distinct from the nephridia even 

 when they replace them in function (Mollusca) ; in the Poly- 

 chseta alone they become variously connected with each 

 other, and in the majority of cases the genital funnel be- 

 comes so intimately fused with the nephridium to form a 

 compound excretory and genital duct, that a study of the 

 adult anatomy alone of these worms would probably never 

 suggest that the organ is formed by the grafting of the one 

 on to the other. 



The Polychgete segment, then, is provided with two organs, 

 the one a genital duct, the other an excretory nephridium. 

 In some cases these organs remain separate, but in most 

 Polychgetes a connection is established between them, a fusion 

 takes place, and the resulting organ may fulfil either or both 

 of their primitive functions. 



Proposed Nomenclature. 



The excretory and genital ducts of the Polychaeta have 

 proved to be of so complicated a structure that it becomes 

 necessary to revise the nomenclature to avoid confusion, and 



