412 WAIL: [VoL. XII. 
out villi, as was the case with Reichert’s ovum. The villi of 
the chorion are from 0.5 to 0.7 mm. long and are branched. 
Upon opening the chorion it was found that the germinal 
vesicle was situated just opposite the edge of the zone of villi. 
About it was much coagulated albumen, which I did not remove, 
and therefore could not obtain good camera drawings. The 
portion of the chorion to which the vesicle was attached was 
cut out and stained with alum cochineal and cleared in oil, but 
even after this treatment it was impossible to obtain any clear 
picture. The specimen was next imbedded in paraffin and cut 
into “sections 10 thick. The {series proved to be pertect. 
From the sections a reconstruction was made in wax, and the 
accompanying Fig. 8 is a sagittal section of it. 
The dimensions of the different portions of the vesicle are 
as follows: 
Diameter,of Stem .5) 00) ee ees eee eo 4am. 
IEF OO Guiel. ofa 4 gid Joe 6 Sg! on! thd (Oye (& 
BGesoVHd sy, CVEAVEHOLES 958 of og) a M6 oo) Bg oo ot Go) a 
AVitelhwOyeaele 5b ol Holo wm a o op ov o Wo) w 
isengethyofinvapinationy We) mee rnin i) tes wee rel Oc Ome 
Widthyofnva cin atlony ames. mn ins i-tal ie ceatO-5ianse 
Diameter of opening of invagination. . . . . 0.03 “ 
The sections and reconstruction show that the embryonic 
vesicle is attached to the chorion by means of a stem (Lauch- 
stiel). The vesicle itself is composed of two layers, between 
which, at a distance from the stem, there are indications of 
blood-vessels in the middle embryonic layer. Just beside the 
attachment of the vesicle to its stem there is a deep, narrow 
invagination of all layers of the vesicle. The walls of the 
invagination are somewhat thicker than those of the surrounding 
vesicle. The accompanying figures give the arrangement of 
the embryonic layers in different portions of the vesicle. The 
invagination is in no respect artificial, as suggested by Graf 
Spee, as the curves are all sharp, and the layers of mesoderm 
and ectoderm are very definitely outlined. The ectoderm has 
the sharp contour of the ectoderm of other young embryos pub- 
lished, and gives the pictures which are familiar to all embry- 
ologists. The entoderm does not extend all around the sections 
as I have pictured it, but has fallen off at some points, and 
