■i2 Developinent and Shape oi' Uriiiil'erous Tubules 



piece, which becomes more clearly defined and does not disappear in the 

 transition from the primary to the secondary S-stage, and this supposed 

 disappearance of the S-middle piece, as the one stage passes into the 

 other, appears to me as the crucial point in Stoerk's argument for the 

 recognition of these two S-stages. In making these statements, I am 

 more especially guided by observations made on reconstructions of 

 tubular anlagen, obtained from developing kidneys of cat embryos vary- 

 ing between 20 mm. and 30 mm. in length and from a human embryo 

 of the seventh month rather than on those made of tubular anlagen de- 

 veloped from the first few generations of renal vesicles of relatively 

 young human and rabbit embryos, as in the former, more generally than 

 in the latter, the S-middle piece differentiates relatively early and con- 

 sequently such tubular anlagen show at a relatively early stage an S-shape 

 when seen in reconstruction. 



Before leaving the consideration of the S-shaped stage in the development of the 

 uriniferous tubule, brief mention may yet be made of a term which was introduced 

 by Colberg and which has now and again been used to designate this stage. Cbl- 

 berg. in an article in which he attempts to controvert some statements made by Henle 

 concerning the shape and structure of uriniferous tubules, which need not he entered 

 upon here, gives also some observations made on the kidneys of a human embryo of the 

 seventh or eighth month and in the course of his remarks states that the " open 

 uriniferous tubules" (straight collecting tubules) divide in the cortex, after having 

 given ofC several branches in the medulla, into four to six side branches, which 

 terminate in the periphery of the kidney either in club-shaped enlargements or with 

 ends which are coiled up several times ; these coiled up ends have about the same 

 size as a fully developed Bowman's capsule and glomerulus of a coiled uriniferous 

 tubule. In the roiled up ends of the straight or open tubule, he was not able at first 

 to detect capillary loops and therefore spoke of them as pseudoglomeriili. Toldt, in 

 discussing a stage in the development of the uriniferous tubule which corresponds to 

 the S-shaped stage, makes use of this term, although in a foot-note, he calls attention 

 to the inappropriateness of it. Hamburger, after discussing the mode of formation 

 of the S-shaped stage, speaks of it, as a stage designated by Colberg as a pseudoglo- 

 merulus, a term whicli, as Hamburger states, has been adopted by the ma.iority of later 

 writers and is retained by him. The term is misleading and inappropriate and need 

 not be retained, as the mesenchyme and capillary loops found in the concavity of the 

 lower S-curve and recognized as the anlage of the glomerulus, form at this stage only 

 a small part of the entire tubular anlage. 



The Genesis of the Diffehent Parts of a Uriniferous Tubule 

 FROM THE Tubular Anlagen of the S-stage. 



The developmental changes undergone by the anlagen of uriniferous 

 tubules, following the stage at which these present the S-shape, affect 

 simultaneously the different parts of the S-shaped structure. In their 

 further growth the tubular portions, embracing the upper S-curve and 

 S-middle piece, elongate, while the bowl-shaped portion, the lower 

 S-curve, enlarges and obtains a deeper concavity; this is accompanied 

 by a proliferation of the vascularized mesenchyme contained within this 

 concavity. We may consider first the changes affecting the tubular por- 

 tion. This, as may be seen, is relatively fixed at its two ends, on the one 

 hand by its attachment to the collecting tubule, on the other by its 

 attachment to the bowl-shaped structure which contains the vascularized 

 mesenchyme and which early forms a relatively fixed structure. Thus 



