482 FRANK E. BEDDAED. 



The wide tubes with an intra-cellular lumen become gradually 

 crowded with nuclei,^ though the boundaries between the 

 individual cells are not to be discerned in my preparations; the 

 lumen, however, is here clearly intercellular, the individual 

 cells being apparently more or less cubical in form. The nuclei 

 are quite similar to those of the portion of the nephridium 

 with an intra-cellular lumen. The tube then bends up towards 

 the epithelium of the gut, and its lumen becomes much con- 

 tracted, owing to the great increase in the size of the cells 

 which form its walls. In this region of the nephridium the 

 cells are quite indistinguishable from those which form the 

 lining membrane of the rectum. 



It seems, therefore, probable that the diverticula of the 

 intestine were developed as diverticula, and that the nephridia 

 afterwards acquired a connection with them, just as the external 

 portion of nephridia opening on to the surface of the body is 

 developed from a separate epiblastic involution." 



In the absence of embryological data, I cannot do more 

 than regard as highly probable the suggestion made above con- 

 cerning the morphological nature of the rectum. The rectum 

 is much more likely to be proctodseum than hypoblastic in 

 origin. If this is not the case, then the facts recorded in this 

 paper have an obvious bearing upon Lang's views (17) of the 

 hypoblastic origin of the nephridia. I should, however, prefer 

 for the present to consider the terminal section of the gut, 

 into which the nephridia open, to be epiblastic in origin. 



So far as I am aware, there has been no description of 

 nephridia connected with the rectum in any other Chsetopod. 



The nearest group in which anything of the kind occurs is 

 the Gephyrea ; in Bonellia, and other forms belonging to the 



• Such a fact as this appears to me to show that the morphological distinc- 

 tion which some have attempted to draw between nephridia with intra-cellular 

 lumen and intercellular lumen, e. g. between those of Oligochajta and 

 Poljchseta, cannot be maintained. 



2 Bergh (16) has, however, denied that this is the case in Criodrilus; 

 according to him the ne[)hridium is entirely mesoblastic, and bores its way to 

 the exterior. 



