422 DISCOVERY REPORTS 



lobular septa (Fig. 24 b). In the centre of every lobe the lobules are less well defined, 

 irregular and polygonal in shape. In still older foetal kidneys (from foetuses about 

 0-5 to i-o m. in length) the lobules are all definitely constricted from one another, and 

 the capsules within them are arranged peripherally, so that their tubules converge 

 towards the neck of the lobule and form secondary urinary ducts joining the main 

 primary system. In the most completely constricted lobules the tubules join together 

 to form a major trunk running through the neck of the lobule. In kidneys at about this 

 stage, then (0-5 to i-o m. foetuses), the substance is divided into a number of pyramidal 

 lobes by the interlobar septa. Each lobe is further divided into an irregular number of 

 lobules by interlobular septa. The lobules are rounded on the outside of the lobes, but 

 irregular and polygonal within (Fig. 24). In kidneys from foetuses about i-o to 1-5 m. 

 in length still further subdivision is found. The rounded and constricted lobules them- 

 selves are seen to be divided into as many as five or six conjoined fan-shaped sections, 

 which presently round off and become definite renculi (Fig. 25 h, 30 B) by the elongation 

 of their necks and the outward growth of their peripheral tissue. The tubules in these 

 incipient renculi join together to form a common duct running through the neck of the 

 renculus, thus forming the tertiary ducts of the main system. The primary ducts have 

 been described as running in the interlobar septa, the secondary ducts run from the 

 lobules to the primary ducts, and the tertiary in the necks of the renculi of which the 

 lobules are composed. 



In the kidneys of a 1-5-2-0 m. foetus (Fig. 26) the lobules are completely divided into 

 their component renculi, which are now circular in outline and have cortices and 

 medullae formed by the peripheral arrangement of the capsules and the convergence of 

 their collecting tubes. From about this point in the development of the kidney the 

 lobule tends to become obliterated as a unit in the architecture of the kidney. With 

 increase in the size of the renculi the lobules lose their identity, and interlobular septa 

 become increasingly difficult to make out. In adult kidneys there is little trace of the 

 original lobular disposition of the renculi and the lobes themselves become difficult to 

 distinguish. The median plane of connective tissue formed by the central core persists 

 in the adult, as does also the mesal slit, although the latter is frequently masked by 

 accumulations of fat within the investments of the organ. 



The lobes remain the architectural unit of the kidney in foetuses of up to 2-0 m. in 

 length. As the renculi increase in diameter and come into contact with one another, the 

 lobules coalesce with one another and become confused, and in foetuses over 2-0 m. in 

 length are difficult to make out. In foetuses larger than 3-0 or 4-0 m. the renculi of the 

 kidney appear to be indefinitely grouped. The disappearance of the interlobular septa 

 is due to the pressure of the renculi against one another tending to squeeze out the 

 boundaries between the lobes and lobules. In yet older kidneys — old adults — the same 

 coalescence and disappearance overtakes the lobes, so that the renculi are the only 

 architectural units that persist throughout the life of the organ. 



A developmental sequence is thus observable in the architecture of the kidney which 

 may be roughly tabulated thus: 



