THE ANATOMY. NEPHRIDIA 49 



that of Lumhricus, is stomodaeum ; hence there is nothing remarkable in the fact 

 that nephridia open into the buccal cavity instead of the exterior, for the buccal 

 cavity is morphologically external. In the case of Octochaetus the correspondence 

 is even clearer; for in that worm the massive Peptonephridia, though they only 

 possess a single aperture apiece into the buccal cavity, open also on to the exterior of 

 the body and as in the case of the nephridia of the succeeding segment by numerous 

 pores. The development, hovrever, happens to show that it is the openings into 

 the buccal cavity which are the primitive openings, the numerous external pores 

 being secondary. The relationship of the modified anterior nephridia to the 'head 

 kidney' of the embryo has already been dealt with. 



2. Anal nephridia. Not only are there undoubted nephridia connected with 

 the anterior end of the alimentary canal ; but in one species of Oligochaeta there 

 are undoubted nephridia connected with the rectal region. In Octochaetus niultiporus 

 I found that a few segments at the posterior end of the body are filled with 

 a dense mass of nephridial tubes which open both directly on to the exterior and 

 into the rectal part of the gut ; I am not, however, certain as to whether this part 

 of the gut is or is not proctodaeum. On the whole, the facts which I was able to 

 get together as to the development of this part of the nephridial system seemed to show 

 that the section of the -gut into which they open is not proctodaeum; on the other 

 hand, probability seems to urge that it is. A remarkable fact about these anal 

 nephridia in Octochaetus is, that they are provided with numerous coelomic funnels. 

 Elsewhere the nephridial system of this Annelid is not in the adult provided with 

 funnels ; the tubes form a branching network, very easy to demonstrate as a network, 

 which communicates from segment to segment and also communicates with the 

 exterior through numerous pores upon the integument; there is thus a direct 

 communication between the interior of the alimentary canal and the exterior through 

 the nephridia ; the nephridial tubules, when they approach the lumen of the gut, 

 open into wider passages, which have a lining of cells precisely like those of the 

 gut ; it would appear that these latter are really diverticula of the gut, though here 

 again the actual development has not been worked out. The occurrence of these 

 nephridia opening into the gut is interesting when they are compared with the 

 respiratory trees of Bondlia and its allies among the Gephyrea. I have also suggested 

 a possible resemblance to the Malpighian tubes of the Arthropoda. The comparison 

 here would be of course with the terminal wider tubes with an intercellular duct 

 into which the actual secretory portion of the tubes open. So far as it is at 

 present known Octochaetus multiporus is the only Oligochaet which possesses anal 

 nephridia'. 



H 



