423 



Lobules 



Lobules 



Renculi 



Renculi 



Renculi 



No stages younger than 0-185 m. C^- musculus) were examined, but it may be sup- 

 posed that the kidneys of the very youngest foetus consist simply of a mass (crescentic 

 in transverse section) of undivided kidney substance composed of the earliest capsules 

 and tubules. 



It is thus possible to trace the development, as architectural units of the kidney, first 

 of the lobe, then of the lobule, and finally of the renculus, and subsequently to observe 

 their disappearance as the renculi grow into contact with one another. 



The capsules and tubules 



We have already seen that in the very young stages the kidney substance is made up 

 of intimately entwined tubules with their renal capsules. Collecting tubes run from 

 them towards the central main urinary duct of the organ. Peripherally the kidney 

 substance is beginning to be divided into lobules (Fig. 23). Each lobule at this stage 

 (Figs. 27, 30 A) consists of: 



(i) Some five or six capsules with their tubules. The number of capsules to a lobule is 

 variable, but it does not usually exceed six. The lobulation, being still indefinite at this 

 stage, does not completely separate the capsules and tubules of one lobule from those of 

 another. 



(ii) One or two main collecting tubes running inwards to the central ureter (Figs. 27, 

 30 A). 



(iii) One or more embryonic areas where new capsules are in process of formation 

 (Figs. 23, 27, 30 A). 



(i) The most perfectly formed tubules and capsules are situated in the deeper parts 

 of the lobule (Fig. 27). There are always three or four large well-developed tubules or 

 capsules having glomeruli, which are apparently functional since they contain blood 

 corpuscles. Besides these there are always two or three other capsules less perfectly 

 formed and more peripherally placed within the lobule (Fig. 27 e 1 ). Their glomeruli 

 are still in various stages of development. The youngest of these stain deeply and con- 

 tain no blood corpuscles, so that they must be supposed to be not yet functional. In 

 older kidneys, in which renculi have formed from the lobules, the renal capsules are 

 arranged peripherally, and their tubules and collecting tubes are radially disposed 

 within the renculus; in foetuses about 2-0 m. in length they join together to form a 

 common duct, the calyx, and a conical papilla is produced at their junction. 



