Lydia M. Dewitt 217
rather regular bands. Polyhedral cells with round or oval nuclei staining more
faintly are scattered irregularly between the columnar cells and form[more
definite masses at the periphery. The sinusoids are distinct with simple en-
dothelial lining and no connective tissue demonstrable, either surrounding the
area or around the intrainsular sinusoids.
I have made no study of fish and
reptiles, but Diamare and Harris and
Gow and others have described large ,
insule in reptilia, and Diamare and
Rennie and others have found simi-
lar structures in fishes, the islands in
these forms having the same structure
as in the types studied by me: certain !
of the very large ones are, however,
constant in position and, in some
species of fish, are independent of f´:
the glandular tissue of the pan-
creas. Fig. s4.--ection of arca of
In general, then, it may be Langerhans from pancreas of
said that areas of Langerhans of frog. X 200.
very similar structure are found in all species of vertebrates
that have been examined. In all species, they consist of cords
or masses of epithelial cells derived from the same anlage as the
pancreatic acini and sometimes retaining their connection with
the glandular tubules. The cells vary somewhat in type in any
one area, but the same or similar types are found in all the species
examined, except the frog and bird; in the bird the cells are
uniformly small and generally oblong, both nucleus and pro-
toplasm staining poorly; in the frog, the predominant cells are
tall and columnar with long deeply stained nuclei, the cells being
packed together in single rows separated by blood-vessels. In
all cases, the cords of cells are separated by large, irregular,
anastomosing blood-vessels, having a complete endothelial wall
and no or very little adventitia. In most forms, the endo-
thelium seems to rest directly on the epithelial cells, and the
connective tissue, when present, appears to be a secondary devel-
opment, as in the somewhat sclerotic, adult human pancreas.
The vessels correspond to Minot's definition of sinusoids. The