THE NEPHRIDIA OP THE POLYOH^TA. 729 



(Trautzsch, 25), the Opheliidse, etc. In others, on the con- 

 trary, the posterior organs may be exclusively genital in 

 function, as in the Terebellid^, Sabellidge, etc. In such 

 cases, the organs which excrete have the glandular canal more 

 highly developed ; whilst those which act as genital ducts only 

 have the funnel region enlarged, and the nephridium reduced. 



Now, if we seek for an explanation of these facts, we are 

 driven to the conclusion that, in a large number of 

 Polychsetes, the so-called "segmental organ" or 

 "nephridium" is in reality formed by the fusion 

 of a true nephridium with a genital funnel; two 

 organs which in certain other Polychsetes,^ in all other Anne- 

 lids, and indeed, so far as we know, in all other Coelomates 

 have always remained distinct. 



That the nephrostome in the Oligochsetes and Hirudinea 

 belongs to the true nephridium, and is developed with it 

 from the same rudiment, has now been proved over and over 

 again (see 10) ; that, similarly, the nephrostome in the 

 Nereidas and Capitellidae belongs to the true nephridium 

 there can be scarcely any doubt, although the steps in its 

 development have not yet been so carefully followed^; that 

 the wide funnel on the anterior end of the segmental organs 

 of the Amphinomidse, Eunicidae, Aphroditidee, Spionid^, 

 etc., does not represent the nephrostome, but is the genital 

 funnel, an organ originating from the coelomic epithelium 

 separately, seems almost equally certain ; and, indeed, may 

 be considered to have been proved by Meyer (22) in the case 

 of the Tubicolous worms. 



Unfortunately we have, as yet, no evidence with regard to 

 the development of these organs in the other families. I can 

 only add one observation of interest in this connection. 



The nephridium of the pelagic larva of Arenicola^ is 



1 These are, of course, the Nereidse (Lycoridea) and some Capitellids. 



^ Ed. Meyer has figured the development of the nephrostome of Nereis 

 from the extremity of the blind larval nephridium (22), 



^ First described by Benham, who was unable to find the nephrostome (1). 

 Since this was written, Messrs. Gamble and Ashworth have described this 



