(1. C^ir] Hubcr 71 



particularly the development of the so-called arcades of the collecting 

 tubules discussed and figured by Von Ebner (p. 1105) will receive con- 

 sideration. The tubules presented in Fig. 17 have been added, as they 

 illustrate very clearly the fact that the first few generations of tubules of 

 kidneys of pig embryos show a relatively very early development of the 

 proximal convoluted portions and of the Malpighian corpuscle, while the 

 loop of Henle develops at a relatively late period ; tubule B, for instance, 

 has attained a length of 1.5 mm. and presents a fully developed Mal- 

 pighian corpuscle, at a time when the bend which is destined to form the 

 loop of Henle (recognized by the fact that the differentiated epithelium 

 of the proximal convoluted portion extends to nearly the top of the 

 bend,) may just be made out. In tubule C, the portion which is recog- 

 nized as the anlage of the loop of Henle presents a number of coils 

 instead of being a relatively straight limb — an appearance which I have 

 observed only in pig embryos. It may here be stated that the formation 

 of the renal vesicles and the differentiation of the S-shaped stage of the 

 uriniferous tubules is for pig embryos essentially the same as for cat, 

 rabbit, and human embryos, as discussed and figured in these pages. 



Hamburger's observations are of interest in this connection. In dis- 

 cussing the differences in form presented by the anlagen of uriniferous 

 tubules in younger and older stages, he states that " the size of the 

 anlage is different in younger than in older embryos and for the same 

 stage of development it will generally be found tliat they are larger in 

 the former than in the latter; especially is this true of the pseudo- 

 glomeruli, which are especially large in young embryos." This, as may 

 have been seen, I have confirmed, adding that they differ, not only in size, 

 but also in shape. He further describes characteristic differences in the 

 development of uriniferous tubules in simple kidney? when compared with 

 those of lobulated kidneys. To quote further : " In animals with simple 

 kidneys (mouse, rat,) the loop of Henle attains considerable develop- 

 ment before the Bowman's capsules become closed so as to form a sphere 

 and this is as true of the first formed anlagen as for those which develop 

 later. In animals with lobulated kidneys (' zusammengesetzten Nieren ') 

 I have found a different condition; in them, the coiled tubules first 

 formed attain considerable length and the Malpighian corpuscles, full 

 development, before a loop of Henle may with certainty be discerned ; the 

 later development, however, is as in simple kidneys." His description of 

 the development of the earlier generations of uriniferous tubules, as 

 observed in embryos of animals with lobulated kidneys (human, pig,) 

 coincides with that here given. In embryos of the cat and rabbit (animals 

 with simple kidneys), I have also observed, as has been stated, a difference 



