The development of the kidney in the rabbit. 293 



no ti'ue pelvis, but one can see that the organ may be divided into 

 a cortical portion where the primary renal vesicles and commencing 

 urinary tubules are situated, and a medullary part, where the ureter 

 and its prolongations with the blastema are still seen. 



Embryo Rabbit of 16 th and 17 th day. 



By the 16 th or 17 th day the Kidney has already assumed most 

 of the adult characters, evagination of the tubules to form a true 

 pelvis is already seen. This cavity forms as an expansion communi- 

 cating on one hand with the ureter, and on the other hand receiving 

 from the Kidney several tubules which can be seen branching and 

 passing in a radiating manner right up to the cortex where they end 

 in primary renal vesicles of which there are now a great many. 

 Already the cortex with its Malpighian bodies and convoluted tubules, 

 its pyramids of Ferrein can be distinguished from the medulla with 

 its collecting tubules and a single set of Henle's loops. The urinary 

 tubules which, in the previous preparation, we saw commencing as 

 buds from the primary renal vesicles, are now fairly developed, while 

 a second set of buds are seen forming at the outer part of the cortex. 

 The organ evidently forms new tubules and Malpighian bodies at the 

 periphery of the cortex, all the young ones are found here while 

 nearer to the medulla the more advanced and older ones are found. 

 The same irregular cavities, the primitive renal vesicles are found 

 invariably at the extreme periphery, and it is from these that the 

 young tubules spring. To these same vesicles the older and more 

 deeply seated tubules pass and they have evidently been thrown off 

 from them as the vesicles divided and pushed outwards in the growing 

 organ. As the vesicles divide and increase in number and push to 

 the periphery, they throw off tubules, while their stalks narrow into 

 cylindrical tubules, the future collecting tubules. 



The process is one which I have found great difficulty in following 

 out in spite of the very excellent material at my disposal. In one 

 section one may perhaps see a vesicle at the periphery giving off its 

 budding tubule, and it is only by a careful examination of other 

 sections in the series that one can make out the tubule passing from 



