184 JOHN LEWIS BREMER 



The evidence here adduced is wholly anatomical, based on the 

 very similarity of tissues for similarity of function which Felix 

 and Weber seem to deny. Moreover it is only the glomeruli 

 of the mesonephros and kidney whose counterparts are recog- 

 nized in the placenta. Further investigations will be necessary 

 to distinguish, if indeed it is found possible to do so at all, the 

 cells of the placenta which correspond to those lining the con- 

 voluted tubules of the excretory organs. 



THE GLOMERULUS 



The essential part of a glomerulus, whether of the mesonephros 

 or of the kidney, is the arrangement of the inner capsule cover- 

 ing the knot of capillary blood vessels. The epithelial cells 

 of this layer, when it is first recognizable, are of a rather tall 

 cylindrical type, as we know from the researches of Stoerk, 

 Huber, and others. With further development the cells become 

 more flattened, but not to the shape of the usual squamous cells, 

 such as those lining serous cavities, with the nucleus sharing 

 in the flattening process, and no part of the cell much thicker 

 than another. The modification consists in the formation of 

 an extremely thin, flange-like process, extending usually from 

 one side of the cell, while the remainder of the cell, including the 

 nucleus, retains its cuboidal shape. At the same time the 

 flanges or plates of adjacent cells seem to fuse so that cell limits 

 can no longer be recognized. In some glomeruli, more commonly 

 those of the mesonephros, the plates at first represent the bases 

 of the cells, each nucleus with its surrounding protoplasm pro- 

 truding beyond the general level (figs. 2 and 3) ; in other glomeruli 

 the surface of the epithelial layer is smooth, and the base uneven. 

 But the first tj^e can easily be, and actually is, converted into 

 the second by the pressure from within the glomerulus of the 

 blood in the capillaries. For it is only in contact with or directly 

 overlying the capillaries that the thin plates are found, while the 

 nucleated portions dip deeper between the vessels, leaving a 

 smooth outer surface. The future development of the glomeru- 

 lus consists of an expansion of the plates, until the nucleated 



