2 Development and Shape of Uriniferous Tubules 



permanent kidneys have their orig'in from buds which arise from the 

 WollKan ducts is now very generally accc[)ted, Kupffer's observations hav- 

 ing been widely confirmed and extended to embrace the different classes 

 of the amniota. While, as just stated, there is a unanimity of views 

 concerning the anlage of the permanent kidney, the views concerning the 

 mode of development and the histogenesis of the tubular and other struc- 

 tural elements are still at variance. 



According to Eemak and somewhat later Kolliker, the development of 

 the permanent kidneys, after their anlage in the buds arising from the 

 Wolffian ducts, proceeds in a manner similar to that observed for other 

 tubular and for alveolar glands, or, as stated by these observers, after the 

 manner of the development of the lungs. The epithelial kidney anlage 

 was said to grow forward and to present an anterior vesicular enlarge- 

 ment, which soon elongates, the anlage differentiating into ureter and 

 primitive kidney pelvis. On this, solid buds and ampulla make their 

 appearance, which in their further growth enlarge and elongate and 

 obtain a lumen, thus forming anlagen for the papillary ducts. These in 

 their further growth undergo division and give origin to hollow buds 

 which form the anlagen for the convoluted (secretory) portions of the 

 uriniferous tubules and the epithelial portions of the Malpighian cor- 

 puscles. According to this view the collecting ducts and coiled urin- 

 iferous tubules are developed by direct budding from the epithelial renal 

 anlage derived from the Wolffian duct. 



On the other hand, Kupffer described a discontinuous origin for the 

 uriniferous tubules. In a sheep embryo of 10 mm. length, he observed 

 a group of cells, clearly differentiated from the surrounding tissue and 

 in close relation with the renal anlage — Kierenkanal — in which he 

 recognized the anlage of the kidney (figured in Fig. 4, PI. XV of his 

 article). In this group of cells Kupffer recognized three zones — a zone 

 consisting of compactly arranged cells in close relation to the renal anlage ; 

 a middle zone of less compactly arranged cells, and an outer zone in 

 which connective tissue fibers were observed. In a sheep embryo of 15 

 mm. length, a differentiation in the middle zone was observed in that 

 the cells were arranged in twisted cords ("Zellen sich in gewundene 

 Streifen ordnen") w^hich were as yet not clearly differentiated. The 

 cells of these twisted cords were not connected with the renal anlagen. 

 These cords were interpreted as the anlagen of the coiled uriniferous 

 tubules. The darker zone of cells immediately surrounding the renal 

 anlage was thought to contribute to their further development. Kupffer 

 could not exclude the possibility that perhaps later generations of 

 tubules had an origin which differed from that here given. According to 



