METANEPHRIC ANLAGE OF CHICK 
427 
These granuloblasts are undoubtedly of local origin, their gradual 
development from the mesenchyme being easily followed. 
Text figure E illustrates the extent of the granuloblastic 
metaplasia which the stroma of the grafted anlage may attain. 
Heavy strands of granuloblasts fill in the spaces between the 
tubules. Granulopoiesis here appears in more advanced stages. 
Mature granulocytes with rod-shaped granules and lobulated 
nuclei have now developed. The intensive changes illustrated 
by this figure do not appear uniformly throughout the whole 
graft. In the central part of the lobules, where the tubules are 
closely packed together and the vascularization is scanty, only 
isolated granuloblasts can be found. A more or less intensive 
granulopoiesis, however, is regularly observed in regions where 
the stroma retains its loose texture and is well supplied by vascu¬ 
lar channels. 
CONCLUSIONS AND DISCUSSION 
1. The metanephric anlage of the seven-day chick embryo, 
when isolated and grafted on the allantois of a chick embryo of 
the same age, not only survives, but grows into a large organ 
and attains a high degree of differentiation.. 
The ureter bud, which at the time of grafting has already begun 
to branch, forms typical collecting tubules. This process is 
exactly similar to that usually described for the formation of the 
collecting tubules of the metanephros developing within the 
embryo. 
The nephrogenous tissue proper also continues its differentia¬ 
tion into the characteristic nephric vesicles. The nephrogenous 
cord, which at the time of grafting appeared in the form of a 
dense syncytium of apparently undifferentiated mesenchymal 
cells, proliferates and differentiates into a secretory epithelium. 
The formation of the lumen of the developing nephric vesicles 
appears to be the direct mechanical result of the secretory 
activity of the cells. The differentiation of the nephrogenous 
tissue leads to the appearance of typical glomeruli, structures 
which at the time of grafting were not present in the anlage. 
The growth and differentiation of the nephric tubules in the 
