412 
RUTH RAND ATTERBURY 
cells later broke down, their cells intermingling with those of the 
connective tissue to form an undifferentiated mesenchymal 
tissue. His conclusions are somewhat surprising. A fully 
differentiated kidney epithelium exercising in the organism a 
highly specialized function, if transplanted into an artificial 
culture medium, not only continues to live, but shows itself 
capable of a series of reversible reactions which bring it back 
to its undifferentiated state. 
Uninterrupted growth of tissue for a considerable length of 
time is not conveniently obtained by the tissue-culture method. 
New data concerning the developmental potencies of the 
nephrogenic tissue might be secured if the nephrogenic anlage 
were isolated from its normal relations within the organism and 
transplanted into a milieu which would permit of its undisturbed 
growth throughout a considerable period of time. At the sug¬ 
gestion of Doctor Danchakoff, I undertook the problem of 
studying the course of development of the metanephric anlage 
transplanted into the allantois of the chick embryo. The 
metanephric anlage of a chick of seven days’ incubation was 
chosen because, 1) at this stage the process of differentiation, 
though started, has not proceeded very far (for example, the 
Malpighian corpuscles are entirely lacking), and, 2) at this stage 
it is relatively easy to separate the metanephric anlage from the 
surrounding organs. 
In this study special attention has been given to the gradual 
differentiation of the specific structures of the, kidney from the 
morphologically homogeneous mesenchyme, which at the time 
of grafting forms the greatest part of the metanephric anlage. 
The development of the stroma has also been studied in detail 
especially with reference to its hemopoietic potency. 
I wish to express my gratitude to Doctor Danchakoff, to 
whom I owe the problem, for her constant help and kind en¬ 
couragement in this work. 
