452 MALL. [Vou. XII. 
to hold any portion of them. This question will be discussed 
in the next paper. 
The extraembryonic coelom has only a short existence, as it 
is already completely obliterated in embryo No. XXII. This 
embryo came to me in an unopened ovum, and on this account 

Fic. 52. — Embryo No. XXII within the Ovum. Enlarged 3 diameters. The villi of chorion are 
outlined on one side of the ovum only. The umbilical vesicle, « v, has become shifted 
around to the dorsal and right side of the embryo. The outline is made from a photograph, 
and is correct in detail with the exception of the attachment of the chord to the chorion. This 
in reality attaches itself to the chorion immediately to the right of the embryo. 
is extremely valuable for this purpose. This embryo is about 
six weeks old, so, reasoning from it, the union of the amnion 
and chorion takes place earlier than is generally believed. In 
embryo No. XLIII, which is about five weeks old, the amnion 
has expanded over the whole embryo and has nearly reached 
the chorion. The earlier stages are given in the sagittal sec- 
tions. They show that the amnion is nearest the chorion at 
the caudal end of the embryo in the earliest stages, and soon 

