Richard Mills Pearce | 44% 
attributed to the island an internal secretion. ‘Their observations were 
made on the pancreas of fish. 
Renaut (5) studied the development of the islands in a single pan- 
creas of a human embryo of the third month (11 to 12 cm. long), and 
found it practically to be identical with that observed by Laguesse in the 
sheep. He also believed that the islands furnish an internal secretion, 
of unknown nature, of more importance in embryonic than in adult life; 
for in the embryo the islands reach their full development, while in the 
adult he considers them to be rudimentary. This is a radical change 
from an earlier view expressed by him (6) that the islands were lympho- 
glandular (points folliculaires) structures. 
Entirely opposed to the above theory of development is that of v. 
Hansemann (7), who states that the islands origimate late in embryonic 
life by a proliferation of the connective tissue cells of the stroma. 'The 
capillaries of the stroma widen and the adjacent cells become richer in 
protoplasm; the vessels assume a glomerular form and the cells an in- 
vesting arrangement similar to that of the perithelium of blood-vessels. 
He finds no relation between the islands and acini, but from the inti- 
mate association between the island and blood-vessels and lymphatics, he 
thinks the islands are concerned in some exchange of substance between 
the blood and lymph. 
Further detailed studies of the development of the islands of Langer- 
hans of the human pancreas I have been unable to find. Different writ- 
ers mention their presence at various periods of embryonic life, thus 
Gartier (8), at three months, Ssobolew (9), at six months, and Stangl 
(10), at about seven months, while Kasahara (11) merely states that 
they are numerous in the foetus. 
Embryology of the Islands——My study of the development of the 
islands has been carried out on the pancreases of twenty-one human em- 
bryos. Some of the material was poorly preserved and unsatisfactory 
for detailed study, but fortunately the better preserved material sup- 
plied the most important phases of the differentiation of the islands. 
The process of development which I have observed would seem to be so 
satisfactory that I have not deemed it necessary to wait for more mate- 
rial before the publication of my results. The study was carried out on 
serial sections, the greater part of the material having been imbedded in 
paraffin, but some were imbedded in celloidin. The sections were 
stained either with haematoxylin and eosin or with safranin and picric 
acid. The following list indicates the source of the material, and the 
length and probable age of the embryo. The length given is that from 
breech to vertex. ‘The method of computing age is that recommended 
