424 
RUTH RAND ATTERBURY 
metanephros until the ninth day of incubation. In the grafts 
the first signs of the glomeruli appear during the third day’s 
growth. Tiny allantoic capillaries grow into the Bowman’s 
capsules, forming the typical glomerular knots so characteristic 
of the normal development. Figure 6 shows well the ingrowth of 
the vessels into the Bowman’s capsules of the graft. The space 
between the Bowman’s capsule and the upper limb of the S- 
shaped tubule (S) described above is occupied by a mass of 
mesenchymal cells. A capillary filled with erythrocytes is seen 
growing into this mass (C). In the larger Bowman’s capsule 
(. B.C .) the vasculoconnective tissue appears greatly increased 
in amount. The capillary network is recognized by the presence 
of erythrocytes and a granular leucocyte. As a result of the 
process of differentiation described above, apparently normal 
Malpighian corpuscles are formed. 
After several days’ growth the metanephric anlage attains 
in the allantois a high degree of organization (figs. 2 and 7). 
Even under low power the tubules and Malpighian corpuscles 
are easily recognized. Huber (’17) has been able to identify the 
various segments of the uriniferous tubules of the adult fowl 
by isolating complete tubules through a process of maceration 
and teasing. It is possible to identify in sections from grafts 
of late stages segments of tubules corresponding to these de¬ 
scribed by Huber for the adult fowl. The secretory tubules are 
readily distinguishable from the collecting ones. The cytoplasm 
of the secreting epithelium is finely granular, and in eosin-azur 
preparations takes a pinkish stain. The cells are low columnar 
and somewhat pyramidal in shape. The segments of Henle’s 
loop appear in grafts of seven or more days’ growth, but never 
grow to their full extent. The collecting tubules, on the other 
hand, are characterized by clear, distinctly basophilic cytoplasm. 
Their cells are cuboidal, with round chromatic, centrally placed 
nuclei. The lumen of the collecting tubules seems wider than 
that of the secretory tubules. Text figures D and E are high- 
power camera-lucida drawings from grafts of six and eight days’ 
growth and show various sections of the Malpighian bodies, the 
secretory and collecting tubules of the grafts, as they appear 
at these stages. 
