No. I.] SPHYRANURA OSLERL 29 



that of one of the cells in question, the cavity of the former 

 passing into the interfilar spaces of the cell. The reason why 

 the connection of the vessels and cells is not more often seen 

 is the same as that advanced above in the case of the renal cells 

 of Sphyranura, — that a series of sections rarely takes the plane 

 of the connecting parts of the excretory vessels and cells. 



There can hardly be any reasonable grounds advanced 

 against accepting the view that the cells of the oral and caudal 

 suckers in Amphistomum are homologous with those of the 

 muscular pharynx in Sphyranura; and as the former, from their 

 connection with the excretory system, are in all probability 

 renal in function, it appears to us to be a correct conclusion 

 that the similar cells in Sphyranura are renal also. 



It seems strange that it is in the oral and caudal suckers only 

 of Amphistomum that all, or nearly all, of these cells are to be 

 found ; while in Sphyranura they are scattered through the body 

 as well, although mainly present where the musculature is most 

 prominent, — in the caudal lamina and in the region immedi- 

 ately anterior to this. It is probable that in the muscular 

 system of these forms the greater part of their metabolism 

 occurs, and in this way we may account for the presence of 

 a large number of renal cells in such organs. This view is 

 supported by the fact that in Sphyranura the caudal suckers 

 (acetabula) completely lack this sort of cells, together with 

 excretory vessels ; but at the same time muscular fibres are 

 absent. The latter are probably present in young or embryonic 

 forms, but in the adult Sphyranurae become changed into those 

 rods which at first sight present a strong resemblance to mus- 

 cular fibres. These rods being skeletal, or merely for the 

 purpose of support, can exercise no metabolic activity; hence 

 the absence of renal cells and excretory vessels. 



The presence of excretory vessels in the caudal sucker of 

 Amphistomum has been held to imply the passive inflation of 

 its frame-work through injection of the vessels with water. The 

 connection of these vessels with the large cells and the struct- 

 ure of the latter point decidedly to a physiological function 

 which must be seriously interfered with if pressure is allowed 

 to act on the internal structure of the cell, which must natur- 

 ally be subjected to the same mechanical conditions as the 

 vessels. 



