90 H. J. FLED HE. 



homologise the left kidney of these forms with tlie single 

 kidney of Monotocards. 



Towards the end of his paper Pelseueer briefly discusses 

 this question of the homology of the Monotocard kidney. 



He first of all sets aside Haller's views, as every sub- 

 sequent worker has differed from that writer regarding tlie 

 relation of gonaduct and kidney. Proceeding next to discuss 

 Perrier's theory, he points out the following weak points : 



1. It necessitates the supposition that the rectum and right 

 kidney have undergone relative translocation. This he finds 

 difficult to imagine. 



2. If we accept Perrier's further conclusion that the Mono- 

 tocard nephridial gland is the remains of the papillary sac, 

 we are forced to assume that in some type the kidneys came 

 to communicate inter se. Having examined Ampullaria, 

 Pelseneer denies that such a connection exists in that type. 



Like the late Mr. Woodward, I cannot see that these 

 objections are really vital. Perrier's theory of the nephridial 

 gland seems to have much in favour of it, as also has the 

 idea that while the Monotocard kidney is that of the Rhipido- 

 glossan right side the opening is that which formerly be- 

 longed to the left kidney, but these are not essential to the 

 theory. If, pending further evidence, we leave aside these 

 additions, the whole of Pelseneer's second objection dis- 

 appears. 



As I have said further above, the frequent existence of 

 the required interreual communication in the more primitive 

 molluscan classes seems to me to minimise the difficulty. 



The question of translocation of the rectum is raised and 

 discussed in rather a new light in this paper, and I venture 

 to think that the conclusions reached very markedly diminish 

 Pelseneer's objection. The rectum has undoubtedly shifted 

 a great deal to the right, such shifting being far more 

 important for the cleanliness of the ctenidium, and therefore 

 for the efficiency of the branchial cavity, even than the 

 rightward shift of the kidney. 



On the whole it does not seem too much to say that, not- 



