718 EDWIN S. GOODRICH. 



reasonable doubt. And so we are inevitably led to tbe view 

 that head-kidneys and posterior nephridia form one homo- 

 logous series of organs, a conclusion also reached by Meyer, 

 and in favour of which I have argued in a previous paper 

 (10). Two of the chief points, urged by those authors who 

 have attempted to show that the head-kidney is an organ sui 

 generis, are that it does not open internally, and that its 

 lumen branches. Now both these characters are common to 

 the nephridia of Nephthys and Glycera. Either the head- 

 kidney is merely a precociously developed nephridium, or 

 Nephthys must be said to have a pair of " head-kidneys " in 

 every segment of its body. A careful study of the first, 

 second, and third nephridium in Polygordius will, I think, 

 dispose once and for all of the view that the " head-kidney " 

 is not a true nephridium. 



Summary of the Most Important Facts described in 

 Parts I, II, and III.^ 



Phyllodocid^ (Part III, p. 669). 



Alciopinaa. — In Vanadis formosa the nephridia are 

 paired, slender, longitudinal tubes, opening ventrally near 

 the base of the parapodium, and continued forwards into the 

 next segment, where they end in a curved blind extremity. 

 Placed at intervals along the anterior third of the canal are 

 bunches of solenocytes. The cell bodies and nuclei of the 

 solenocytes are massed together at the free distal ends of the 

 tubes. Long flagella work down the tube into the lumen of 

 the canal, which is ciliated, and ends posteriorly in a slightly 

 dilated chamber before the external pore. Cilia are situated 

 on the coelomic surface of the nephridial duct, in the vicinity 

 of the solenocytes ; by their action they renew the fluid in 

 the neighbourhood of the tubes. 



The nephridia of other Alciopids examined, Alciope and 

 Asterope, are of practically the same structure; but the 



1 Part I appeared in vol. 40 (1897), and Part II in vol. 41 (1898) of this 

 Journal ; see the table of contents at the end of this paper. 



