G. Carl Huber ■ 47 



portion of a developing uriniferous tubule. Of two uriniferous tubules 

 of apparently the same - stage of development, the distal convoluted 

 portion of one may be as long again as that of the other. This is to 

 a certain extent true of uriniferous tubules reconstructed from embryos 

 of the same species, more clearly seen when those reconstructed from dif- 

 ferent species are compared. As a rule in reconstructions of uriniferous 

 tubules showing early stages of development obtained from human 

 embryos, the distal convoluted portion is relatively longer than in such 

 obtained from cat and rabbit embryos. Compare for example J of Fig. 

 4 with H of Fig. 6, two tubules showing about the same stage of 

 development. The distal convoluted portion of a uriniferous tubule is 

 generally found just above the Malpighian corpuscle of the respective 

 tubule, a relation which is fairly constant even for later stages of 

 development, and will receive further attention in considering these. 

 During the time in which tubular portions of uriniferous tubules de- 

 velop as above described, the anlagen of the Malpighian corpuscles of 

 hemispherical shape change to corpuscles of spherical shape. Tliis 

 is accomplished by a growing upwards and a turning in of the border 

 of the double-walled epithelial structure representing the anlage of 

 Bowman's capsule and by a growing outwards of the fold which arises 

 from its inner wall in the region of its attachment to the tubular 

 portion, this fold being continuous with its border. In this way the 

 opening into the double-walled structure is gradually narrowed until 

 only a relatively small opening remains, at which, as in earlier stages, 

 the inner wall becomes reflected into the outer wall. This opening into 

 the double-walled spherical structure as thus developed and which may 

 now be known as a Bowman's capsule, is situated in its outer and upper 

 portion. During this time, the mesenchyme and vessels recognized 

 as the anlage of the glomerulus differentiate into a definite glomerulus, 

 the small opening leading into the cavity of Bowman's capsule serving 

 for entrance and exit of the afferent and efferent vessels of the glomerulus, 

 these being accompanied by a small amount of connective tissue. A 

 Malpighian corpuscle of this stage of development presents essentially 

 the same shape as a fully developed corpuscle and differs from those 

 found in post-foetal life, aside from certain details in cell differentiation, 

 only in being smaller. The relative degree of development of a Mal- 

 pighian corpuscle and the tubular portion of a uriniferous tubule, when 

 the extent of the development of the former is compared with the extent 

 of the development of the latter, varies somewhat for different tubules 

 reconstructed from embryos from the same species of animals; more so 

 when developing uriniferous tubules obtained from embryos of different 



