4 Dovoloi)iiient and tShape of Lrinit'eious Tubules 



Fiirbriii<:ei\ 78: Kiiierv. 83; Wiedersbeim, 90; Hamburger, go; Weber, 

 97; ('liievitz, 97; Kil)l)rrt. 99; Herring, 00; Scbreiner,' 02 ; Haugh, 

 03 ; Keibel, 03 ; Felix, 04. Tbese observers, while expressing a unanimity 

 of view concerning the separate anlage of tbe tubular system of the 

 permanent ki(biey, are not in accord as to the histogenesis of the tissue 

 from which the tul)ules are differentiated. 



Certain observers, among whom may be mentioned Sedgewick, 80; 

 Eiede, 87 ; Hoffmann, 89 ; Gregory, 00, may be separately grouped, since 

 thev assume an intermediate position inclining toward a separate anlage of 

 the tubules but assuming a histogenetic relationship between the tissue 

 from which the tubules are developed and the epithelial renal anlage. 

 This brief array of the contributors to the literature under consideration 

 may serve as an introduction to a fuller discussion of certain of the more 

 recent contributions; these and others will receive further mention in 

 presenting the results of my own investigations. 



Of the recent contributions to our knowledge of tlie development of the permanent 

 kidney, the article of Schreiner deserves special mention. The results presented are 

 based on observations made on representatives from the different classes of amniota 

 and embrace a study of the origin and development of the tubules of the Wolffian body 

 and of the anlage of the different constituent elements of the permanent kidney. I find 

 it somewhat difQcult to give a brief summary of this article, which is accompanied by 

 numerous illustrations of sections, of profile reconstructions and of reconstructions after 

 the Born method. The discussion of his own observations, he begins for each type 

 investigated with a consideration of the histogenesis of the tubules of the Wolffian 

 body, following this by a discussion of the origin and development of the permanent 

 kidney in each type. Schreiner traces the origin of the tubules of the Wolffian body 

 to a cell-mass which he designates as the nephrogenic tissue (a term suggested by RabI), 

 which is identical with tlie blastema of other authors. This nephrogenic tissue has its 

 origin in the intermediate cell-mass and extends as an unsegmented cord along the mesial 

 and dorso-mesial side of the Wolffian ducts to their termination in the cloaca. From the 

 cells of this cord of cells, which increase in number by division, are differentiated the 

 tubules of the Wolffian body. These appear first in the anterior segments and, as 

 development proceeds, also in the posterior segments. The differentiation of tlie tubules 

 of the Wolffian body does not, however, extend to the posterior limits of the nephrogenic 

 tissvie, but ceases a number of segments anterior to the termination of the Wolffian 

 ducts and nephrogenic tissue. The permanent kidneys have their origin in evaginations 

 (one for each side) from the dorso-mesial wall of the Wolffian ducts not far from their 

 termination in the cloaca. These evaginations grow dorsally into the posterior portion 

 of the nephrogenic tissue and in doing so become capped with the nephrogenic tissue. 

 The evaginations, or as they are known, the renal anlagen, renal ducts or Nierengiinge, 

 at first present a bulbous extremity. Tliis elongates in an antero-posterior direction 

 and develops buds and ampullse. In the meantime, the nephrogenic tissue, which at first 

 surrounds the bulbous extremity of the renal anlagen as a compact cell-mass, breaks 

 up into several cell-masses, each of which caps one of the primary branches of the 

 renal anlagen, at the same time losing its connection with the nephrogenic tissue from 

 which are developed the tubules of the Wolffian body. This portion of the nephrogenic 

 tissue Schreiner now terms the metanephrogenic tissue in contradistinction to the meso- 

 nephrogenic tissue. The metanephrogenic tissue, in the majority of the forms studied 

 by Schreiner may be differentiated more or less clearly into an inner zone composed of 

 cells more compactly arranged and presenting other characteristic features and an 

 outer zone, tlie cells of which are less compactly arranged and approach in appearance 

 mesenchymal tissue. Schreiner further shows that the epithelium of the ureters and 

 pelvis of the kidney as also the collecting tubules to their terminations are developed 

 from the renal anlagen ( >Jiereng;inge), while the secretory portion of the nriniferous 

 tubules from their termination in the collecting tubes to and including the epithelial 

 portion of Bowman's capsule are differentiated from the inner zone of the metanephro- 

 genic tissue, the interstitial tissue and the capsule of the kidney developing from the 

 outer zone. Schreiner's observations, accompanied by a very hill discussion of the 

 literature and substantiated by numerous figures, appear to argue conclusively for a 

 separate anlage of the tubules of the Wolffian body and the secretory pcu'tion of the 



