METANEPHRIC ANLAGE OF CHICK 
419 
shows a cross-section through a tubule filled with a mass of 
degenerating erythrocytes. Numerous epithelial cells lining the 
tubule are seen with cytoplasmic processes directed toward the 
mass of erythrocytes. In the lower part of the tubule may be 
seen actually ingested pieces of hemoglobin-containing cyto¬ 
plasm (I . Hb.-c .). Above, the ureteric epithelium has ingested 
an erythrocyte, the nucleus of which has not yet disintegrated. 
Phagocytic activity by kidney cells of the frog has been described 
by Smallwood (’08) inacaseof hemorrhagic kidney. He observed 
red blood corpuscles in the lumen of tubules and particles of 
hemoglobin-containing cytoplasm within the epithelium. Small¬ 
wood does not state in what kind of epithelial cells he found the 
ingested material, but judging from his figures it must have been 
the ureteric epithelium of large collecting tubules. The presence 
of degenerating corpuscles in the lumen of the ureteric tubules 
is frequent in the early stages of kidney growth in the allantois, 
but they are never found in grafts of six or more days’ growth. 
One might conclude, therefore, that the process of digestion of 
the erythrocytes present in the tubules has been completed by 
this time. 
2. Growth of the nephric epithelium. As stated above, the 
nephrogenous tissue at the time of grafting consists of a dense 
mass of mesenchymal cells clustering thickly about the branches 
of the ureteric diverticulum. This tissue likewise survives and 
grows in the allantois. It reaches a high degree of differentiation 
in the formation of typical nephric tubules. 
In figure 3 the nephrogenous tissue appears as a continuous 
mantle of cells covering the forked terminations of the primary 
ureteric branch. The cells in immediate contact with the ure¬ 
teric epithelium are thickly packed and arranged vertically with 
respect to the ureteric epithelium; the outer, more distal cells, 
are looser and are grouped concentrically about the more proxi¬ 
mal cells. This arrangement of the nephrogenous tissue cor¬ 
responds to that present in the anlage at the time of grafting 
(fig- !)• 
As may be seen in figure 3, several structural differences exist 
between the proximal and distal cells of the nenhrogenous tissue. 
THE AMERICAN JOURNAL OF ANATOMv. VOL. 31. NO. 4 
