498 The American Naturalist. [May, 
cells of these evaginations fold in and form the tissues of the pan- 
creas. ‘The three portions separated at first subsequently fuse into a 
single organ. The three openings into the gut, however, undergo 
several changes. In the adult Urodeles there is a forward opening for 
the pancreatic gland into the intestine near to the pylorus. This comes 
from the dorsal evagination of the embryo. ‘There are in the adult 
Urodeles two or more other openings behind this, some of which fuse 
with the duct from the liver (ductus choledochus). The posterior 
openings result from various combinations of the two ventral (right 
and left) evaginations. In the Anuran the adult has no anterior 
opening of the pancreas near the pylorus. In the embryo, however, 
there is one (the dorsal), as in the Urodeles, but it is subsequently 
lost. The two ventral (or side) evaginations unite with one another 
and form a single opening, which subsequently fuses with that of the 
ductus choleodochus, as in the adult. 
Embryology of Glires.—M. Duval has published another of his 
series of papers on the development of rodents, entitled, ‘‘ Le Placenta 
des Rougeurs.’?4 The young stages of the mouse are described. 
Sections through the whole gravid uterus were made in most cases. 
The earliest stage described had a single layer of ectoderm cells sur- 
rounding a central cavity. Underneath one portion of this layer were 
-a very few large granular amceboid-like cells, which subsequently spr ead 
out beneath the ectoderm to form the endodermal lining of the vesicle. 
Above this portion in later stages the ectoderm thickens greatly, result- 
ing in a solid plug in which a cavity subsequently appears to fonn a 
cavity of the amnion and the ectoplacenta. The relation subsisting 
between this ectoplacenta and the allantois on the one side and the 
uterine walls on the other form the substance of the latter part of the 
paper. The problem of the inversion of the layers in the mouse and 
rat were discussed in a preceding paper (see abstract in AMERICAN 
NATURALIST for April, 1891). 
4 Journal de l' Anatomie et Physiologie, Jan.-Feb., 1891. 
