PRIMARY MALIGNANT GROWTH OF THE KIDNEY 163 
from the peripheral cells of the pseudo-cysts the outlines of the latter are interrupted 
(Figs I and II) ; specimens which are embedded in sarcomatous structure shew no 
definition except where the central squamous cell passes into the polyhedral type, the 
latter passing insensibly into the somewhat smaller and rounder sarcoma cell. In 
some specimens, however, even thus embedded there is a single row of cubical cells 
with large nuclei outside the squamous cells. 
The peripheral cells of the pseudo-cystic bodies, therefore, give origin to 
sarcomatous elements. But the sarcomatous elements in this main central lobe which 
we are now considering are not exclusively derived from the pseudo-cysts. Adjacent 
to many of these, Tubules lined by cubical cells are seen, cut in various directions. 
Their outlines are interrupted by proliferative protrusions of these cubical cells, which, 
growing outwards, become sarcomatous in type. Scattered tubules, the cells of which 
are proliferating in this way, are also seen away from the proximity of the pseudo-cysts. 
The muscle and fibrous tissue cells forming the strands, are in connection with 
the cells of the limiting layer of the pseudo-cysts for the most part. 
Apical Lobe — This portion of the growth shews microscopically a much 
smaller proportion of fatty tissue than the central mass. Pseudo-cysts are seen 
here also, but none are degenerated to the stage of complete fibrillation, but 
consist centrally of large squamous cells with a fine reticulum. Sarcomatous 
tissue forms the main mass of this lobe, developed as before from the outer 
layers of the pseudo-cysts. However, tubules are more numerous here, and 
most of the sarcoma cells originate from the cells of these (Fig. IV). In fact the 
outlines of these tubules are usually quite irregular and broken. Muscle and 
connective tissue cells are distributed throughout the sarcomatous tissue. 
Sections from the inferior lobes of the growth shew an almost uniform 
sarcomatous structure, with some interstitial fatty tissue. Throughout the structure 
the outlines of scattered and irregular tubules are seen. None of the pseudo-cystic 
formations were seen in the sections from this portion of the growth. 
The vascularity of the different lobes varies. Where the sarcomatous cells 
are most numerous the vessels are many and large ; on the other hand, where fatty 
tissue predominates they are small and very few in number. 
From this description of the histology of the tumour it will be seen that the 
whole structure is traceable to the cells of certain tubules, and what have been pro- 
visionally termed pseudo-cysts. The significance of these two elements must now be 
considered. The kidney, with the exception of the collecting tubules, is developed 
from a portion of the intermediate cell mass, posterior to the Wolffian Body, and the 
first elements differentiated are the Malpighian Corpuscles and convoluted tubules. 
These both originate as solid masses of mesoblastic cells, and are subsequently 
hollowed out, the Corpuscle developing at the blind end (that not in connection with 
the peritoneal involution). The foetal Malpighian Corpuscle consists of a limiting 
