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RUTH RAND ATTERBURY 
cranial or its caudal part. The window was closed and sealed 
with paraffin and the egg returned to the incubator. The 
grafts were permitted to grow through various stages ranging 
from one to twelve days. Helly’s fluid was used for fixation and 
celloidin for embedding. The blocks were cut in serial sections 
and stained in eosin-azur. 
OBSERVATIONS 
A. Structure of the metanephric anlage at the time of grafting 
In order to determine the extent of growth and differentiation 
of the metanephric anlage in the allantois, a careful study was 
made of the structure which the anlage presented at the time 
of grafting. As seen in text figure A, the ureteric bud at this 
stage has already grown into the tissue of the metanephrogenic 
strand and has given rise to two groups of short branches, a 
cranial group and a caudal group. These branches constitute 
the primordia of the collecting tubules of the kidney. The 
ureteric branches of the caudal group are apparently in a slightly 
more advanced stage of development than the cranial. They 
seem somewhat longer and in several instances they have begun 
to give off secondary branches. Figure 1 is a photograph from 
a section of the metanephric anlage of a seven-day chick embryo 
and illustrates the extent of differentiation at this stage. The 
figure represents a section from the caudal, and, therefore, 
the most highly differentiated, part of the anlage. The ureter, 
cut longitudinally, appears in the form of a tubule with a dis¬ 
tinct lumen. This tubule has given off a primary ureteric branch 
which has started a further dichotomous division, forming in 
this way secondary branches. The lumen of both the ureter 
and its derivative is lined with simple columnar epithelium. 
The nuclei of the epithelial cells are large and have distinct 
nucleoli. Mitotic figures at this stage are found in large numbers. 
Text figure A shows the branches of the metanephric divertic¬ 
ulum thickly covered with dense masses of cells. In sections 
these appear in the form of a mantle of mesenchymal cells in 
close apposition with the branches of the ureter bud. These cells 
