428 
RUTH RAND ATTERBURY 
grafts may reach a high degree of organization. In older grafts 
convoluted tubules and segments of Henle can be identified. 
The process of growth and differentiation of the secretory part 
of the kidney on the allantois does not differ from that which 
normally takes place in the undisturbed kidney anlage. 
The fact that the metanephric anlage of a seven-day chick 
embryo, when isolated from its normal relations within the 
organism and transplanted into the allantois, continues to 
differentiate into characteristic nephric tubules seems to indicate 
that at this time the young anlage has already become specifi¬ 
cally organized. Contrary to the results obtained by Champy, 
the parts of the anlage already differentiated (ureteric epithelium, 
epithelially arranged cells of the nephrogenous tissue) do not 
undergo a series of reversible changes, but show a marked 
capacity to retain their epithelial arrangement and to differentiate 
still further. Moreover, the apparently undifferentiated part 
of the anlage, which at the time of grafting appeared in the 
form of a dense syncytium of mesenchymal cells, showed the 
ability to acquire an epithelial arrangement and to form typical 
nephric tubules. The process of differentiation proceeds to such 
an extent that even the allantoic capillaries are induced to form 
t}^pical glomerular knots within the concavities of the 
Bowman’s capsules. The allantois seems to be as favorable a 
medium for the growth and differentiation of the metanephric 
anlage at this stage as its normal environment within the or¬ 
ganism. The grafted anlage may attain the same general form, 
size, and structure as that of the normal kidney of corresponding 
age. 
Not only does the transplanted metanephros acquire the 
structure of the normally developing kidney, it also, as far as 
histological evidence can determine, develops physiological 
activity. This development of both structure and function 
in the grafted anlage takes place despite the fact that it can be of 
no possible use to the general organism, since there is no outlet 
in the transplanted metanephros whereby the graft can get rid of 
the products of its secretory activity. Champy has ascribed the 
process of dedifferentiation of the metanephros in his cultures to 
