30 Devclopniciit and Shape of rriiiiferous Tubules 



shall designate as renal vesicles (following Emery, not to l)e confused 

 with the primitive renal vesicles as described by Haycraft) are differ- 

 entiated from the inner zone of the metanephrogenic tissue in the man- 

 ner above described. ''J'he first renal vesicles differentiate in the types 

 of embryos studied liy lue simultaneously with the anlage of the two 

 branches into whicli the branches (primary collecting tubules) of the 

 primary renal pelvis divide. That the renal vesicles have no connection 

 with the primary collecting tubules may generally be made out by tracing 

 these structures through a series of relatively thin sections.; wax recon- 

 structions of the primary collecting tubules and of the renal vesicles give, 

 however, conclusive evidence of their independence. 



Investigators who hold that the urinifei'ous tubules are developed by a process of 

 budding from the primary, secondary and further branches of the epithelial renal 

 evagination do not recognize the renal vesicles as here described. As they can not 

 have escaped their notice entirely, it must be assumed that they are regarded by them 

 as continuous with the developing collecting tubules at all stages of their development 

 and that they were thus interpreted as solid or hollow buds of the collecting tubules. 

 Few of the contributions to which reference is here made contain satisfactory accounts 

 of the earliest stages of the development of the uriniferous tubules nor are they 

 accompanied by figures which clearly portray these stages. The figures presented 

 are, in the great majority of instances, of stages where a direct continuity between 

 collecting tubule and uriniferous tubule can not be questioned. Certain of the 

 figures to which reference is here made showing earlier stages of kidney develop- 

 ment deserve brief consideration. We may mention Fig. .581 of Kolliker's Bntwickelungs- 

 gescliichte des Menschen und Hoheren ' Thiere (1879), which shows a longitudinal 

 section of the kidney of an embryo rabbit 16 days old. In this figure are shown 

 several primary collecting tubules ('• Fndsnrossen des Ureters Oder Ampullen'"), 

 showing T or Y-shaped division of their distal ends and at least seven renal vesicles, 

 if I may be allowed to interpret the figure in the light of observations made on my 

 own sections of rabbit embryos of about corresponding age. In the accompanying text. 

 Kolliker states that by further growth of the branches of the collecting tubules, these 

 form the uriniferous tubules : no mention is made of the renal vesicles. In Figures 

 1. 2, 3. and 6 (of Plate XXIV) of Tjowe's article, sketches of the entire kidney, as 

 seen in longitudinal section of rabbit embryos of 5, 10, 20, and 50 mm. length 

 respectively are shown numerous renal vesicles in various stages of development in 

 close relation with a tissue, which from its form and position must be regarded as 

 the inner zone of the nephrogenic tissue. Liiwe, who recognized the cell-masses, 

 has interpreted them as renal vesicles and traced their origin to Braun's cords, stating 

 that from them is developed the endothelium of the capillaries of the Malpighian iiodies, 

 while all parts of the uriniferous tubules with the epithelium of Bowman's capsule 

 are derived from the primary ureter branches. Again in Figs. 40 and 41 of Strahl's 

 communication (kidneys of human embryos of 28 mm. and .35 mm. length respectively) 

 the inner and outer zones of the nephrogenic tissue and renal vesicles are recogniz#d. 

 Stoerk's series of figures grouped under Fig. 2, giving in a " semi-schematic " way the 

 development of the ends of the " ur<>ter branches " and the anlage of the Malpighi.in 

 bodies (Nieren-korperchen) show that he has not observed the renal vesicles, but. as 

 No. 4 of this series of fisjures would indicate, he has interpreted the renal vesicles as 

 buds of the ureter branches, as the position of the downward growing buds, as there 

 figured, coincides with the relations shown by renal vesicles and pi'imary ureter 

 branches at a corresponding stage of development. Mention was made of Stoerk's view 

 of the anlage of the uriniferous tubules on page 5. Toldt, whose observations are fre- 

 quently quoted as giving conclusive evidence of the development of the uriniferous 

 tubules by a process of budding or further growth of the ureter branches, removed the 

 kidneys from young embryos, stained them in hrematoxylin or carmine, cleared them in 

 turpentine and placed them on a slide as a whole. In such preparations, the primary 

 branches of the ureter could be traced without interruption to the periphery of the organ 

 where they terminated in enlargements. A further examination of the ureter branches 

 designated by Toldt as " Zellsprossen " with higher magnification showed that they 

 grew forward first as solid buds which later attained a lumen. In Fig. 1 of the 

 plate accompanying his article (kidney of cat embryo l.S mm. in length) is reproduced 

 such a preparation. This shows however only ureter, primary renal pelvis and its 

 primary branches, surrounded by kidney blastema and gives no evidence of the anlage 

 of the uriniferous tul)ules. It should be remembered that it is conceded by the majority 

 of observers that the epithelium of the primary renal pelvis and its branches is derived 

 from the renal evagination by growth and budding. The figures given by Toldt 

 and obtained from sections and teased preparations to show the anlage of the urini- 

 ferous tubules are of more advanced stages. It must, therefore, be stated that the 

 method selected bv Toldt to show the anlace of the urinifei-ous tubules is not a suit- 

 ai)le one. The figures given by P.ye, Nagel, Oolgi, Minot, Haycraft, Von Ebner, and 

 Disse show that thej' are dealing with developmental stages that do not represent 



