G. Carl Huber . 27 



appearance of a crescent with concavity directed upwards toward the 

 periphery of the kidney. Reconstructions of tubular anlagen of this 

 stage show that this portion presents the shape of the bowl of a spoon or of 

 a saucer with the concavity turned toward the other parts of the anlage. 

 In making this comparison, it is to be understood that this structure is 

 not solid, but double-walled, the enclosed space, which is continuous with 

 the lumen of the other parts of the anlage, having a similar shape. At 

 this stage in the development, the upper concave wall of the structure is 

 composed of columnar cells, while the lower or convex wall is composed 

 of cubical cells. Both in the series of sections of the tubular anlage 

 shown in B of Fig. 3, and also in the reconstruction of the same, B, 

 Fig. 4, it may be clearly seen that it is not continuous with the ampullar 

 enlargement of the collecting tubule. It is in close contact with it but 

 not continuous with it. In C of Figs. 3 and 4 is shown a tubular anlage 

 which is only slightly further advanced in its development than the one 

 shown in B of the same figures. The section sketched shows, however, 

 a continuity of the lumen of the tubular anlage and that of the ampulla 

 of the collecting tubule, although, as is evident from the sketch, the 

 place of union of the two previously discontinuous parts may yet be 

 made out, partly by reason of the position of the nuclei of the respective 

 cells, also because there is as yet a slight constriction at the place of 

 fusion, this being not as yet complete. The modus operandi of this 

 union between tubular anlagen and collecting tubules has been discussed 

 by Schreiner, who states that he has observed in the tubular anlagen or 

 in the ampullar enlargement of the collecting tubule at a stage which 

 he has recognized as just previous to a stage in which there is union 

 of the two, a cell in mitotic division or cells which by their structure and 

 staining show that they have just completed division. This division of 

 cells at the place of contact of the upper end of the tubular anlage and 

 the ampulla of the collecting tubule, Schreiner associates with the fusion 

 of these parts and with the formation of a continuous lumen. This 

 stage is rather difficult to find, as it is not readily recognized unless the 

 respective tubular anlage is seen in a favorable sagittal section. In the 

 tubular anlage, a section of which is here shown, there is no evidence 

 which would indicate that one or more of the cells situated at the place 

 of its junction with the collecting tubule had just completed its division. 

 In my own preparations I have not found cell division at the place of 

 contact between tubular anlagen and collecting tubules more frequent 

 than in other parts of these structures in a stage which might be inter- 

 preted as just prior to a fusion of these structures. My own observa- 

 tions would, therefore, confirm only in part those of Schreiner as con- 



