THE DEVELOPMENT OF THE ISLANDS OF LANGERHANS 
IN THE HUMAN EMBRYO. 
BY 
RICHARD MILLS PEARCE, M. D. 
From the Pathological Institute, University of Leipzig, Prof. Marchand, Director, 
and 
The Pathological Laboratory of the University of Pennsylvania. 
With 3 Text FIGURES. 
The investigations ‘upon the pathology of the pancreas carried out 
during the past several years have had, with few exceptions, for their 
definite object the determination of the existence of an internal secretion 
with which the islands of Langerhans and carbohydrate metabolism 
might be brought into harmony. The great importance to pathology of 
the studies carried out upon these subjects was to be found in the estab- 
lishment of an anatomical and physiological basis for diabetes mellitus. 
That this undertaking has been followed by a good measure of success is 
shown by the important contributions to the pathology of the pancreas 
in diabetes by Opie, Ssobolew, Weichselbaum and Stangl, Wright and 
Joslin, and Herzog, as well as the experimental studies of Ssobolew and 
Schulze. Now that the relationship of a highly important physiological 
function to the islands of Langerhans seems to be established, it is de- 
sirable that the question of the histogenesis of the islands be put on a 
firm and definite basis. If the islands are wholly independent struc- 
tures, as conceived by v. Hansemann, evidence of this fact should be 
forthcoming from a study of their development; if, at their origin, they 
are indistinguishable from the proper glandular structure, evidence of 
this fact should be found in the same study.. If the latter conception is 
the true one, as indicated, but not established, by the studies of Laguesse, 
Renaut, and Diamare, then the period and the manner of the differentia- 
tion should be open to demonstration. The study of the development of 
the islands in the human pancreas has been very imperfectly pursued, 
Renaut, as far as I can discover, alone having examined an early specimen. 
I have been fortunate in securing during the past year a series of 
specimens of the human pancreas which were suitable for a systematic 
study of the development of the islands of Langerhans. This study 
