72 Development and Shape of Uriniforous Tubules 



between the tubules first formed and those which develop later. As I have 

 not reconstructed the iiriniferous tubules of embryos of the mouse and 

 rat, I am not in a position to judge Hamburger's observations as concerns 

 these; he is, however, in error when he generalizes from such observa- 

 tions. He further states that " In young embryos of species with lobu- 

 late kidneys (human, pig, beef), the most fully developed Malpighian 

 corpuscles are absolutely larger than in older embryos and this is also 

 true of the diameter of the tubuli contorti. In animals with simple 

 kidneys (mouse, rat), this not the case." In this also, my own observa- 

 tions do not confirm him, as in embryos from both types of animals I 

 have found the Malpighian corpuscles and the proximal convoluted por- 

 tions (tubuli contorti) of the first formed tubules larger than of those 

 which develop later; in tlie rabbit, this is especially so. (See Fig. 14.) 

 In a discussion of his observations. Hamburger states that it may be possi- 

 ble that in tubules showing early development of the coiled portions and 

 Malpighian corpuscles with absence of a distinct loop of Henle, these may 

 develop as the kidney development proceeds. " Since without doubt, how- 

 ever, the first generation of coiled tubules of lobulated kidneys degenerates, 

 the supposition is permissible that it is particularly the atypical tubules 

 that disappear; conclusive evidence of this, I am however unable to 

 present." Eiedel (I quote from Hamburger) who also recognized the 

 large size of the Malpighian corpuscles and tubuli contorti of the first 

 formed tubules, states that these become smaller as development proceeds. 

 Kolliker, whose description is based largely on rabbit embryos, quotes 

 Eiedel (page 952) as describing a degeneration of the Malpighian corpus- 

 cles and tubuli contorti first formed, for which he states there is no 

 evidence. Emery, on the other hand, who studied the development of the 

 kidney in goat embryos, states that he did observe evidence of a breaking 

 down of the first formed tubules. Hamburger attempts to harmonize 

 the conflicting views of Kolliker and Emery by stating that in embryos 

 of animals with simple kidneys, there is no evidence of a breaking down 

 (zu Grundegehen) of the first formed tubules, while in embryos of 

 animals with lobulated kidneys, it is the atypical tubules wliicli atrophy 

 and disappear. My own observations lead me to say that neither in 

 embryos of animals with simple kidneys nor in those with lobulated 

 kidneys have I obtained evidence which would lead me to conclude that 

 arfy of the uriniferous tubules atrophy and disappear in the course of 

 development. Tubules with relatively short loop and well developed 

 Malpighian corpuscles and proximal convoluted portion, I have observed 

 in embryos of animals with simple and with lobulated kidneys; in such 

 tubules, as will be stated in presenting the more advanced stages of devel- 



