6 
Blenkins, on an Early Human Ovum* 
any abnormal state of its envelopes^ nor on malformation ot 
disease of the embryo itself. There is a slight amount of 
coagulum at opposite points of the chorion^ but that, in all 
probability,, was formed at the time of its separation and ex- 
pulsion from the uterus. The ovum (fig. 1) when entire was 
of an oval shape, and its dimensions were half an inch in its 
long diameter and three eighths of an inch in its shortest. 
The external surface of its outer membrane or chorion was 
thickly beset with villi more closely aggregated in some parts 
than others. This membrane was laid open after the speci- 
men had been macerated in tolerably strong alcohol, with the 
view of hardening it, so as to render its examination more 
easy — a proceeding which I am now convinced is a bad one, 
and should much prefer, if I met with another, to display the 
several parts under water in its recent state, as the action of 
the spirit has the effect of rendering the membranes opaque 
and causing them to collapse, and, in all probability, the first 
incision will divide or detach either the umbilical vesicle or 
the allantois ; the former occurrence unfortunately happened 
in this instance, and though the relation of the vesicle to the 
embryo was clearly seen and traced, its division has some- 
what injured the specimen. Between the chorion and amnion 
lay the umbilical vesicle or vitelline sac, relatively of large 
size, oval in shape, and measuring one eighth of an inch in 
its longest diameter ; this presented a shrivelled or corrugated 
appearance, and its contents were coagulated by the action 
of the spirit. A most distinct attachment or prolongation 
from the vesicle into the abdomen of the embryo existed, and it 
seemed also to be adherent to the amnion at this point ; there 
is no duct which can be properly so termed, but there is a 
slight constriction at the point of junction with the embryo. 
The vesicle did not occupy the whole of the space between 
the amnion and chorion, between them there was a consider- 
able interval, intersected by slender, soft filaments, forming a 
very delicate reticular tissue, to which Velpeau has assigned 
the name of corps reticule ; this I detached in order to bring 
the exterior surface of the vesicle more distinctly into view, 
as this minute web of albuminous filaments, from the con- 
nection existing between it and the chorion, in some measure 
concealed it. Immediately investing the embryo, and closely 
applied to it everywhere, was a very delicate membrane, 
visible only when placed under the microscope, which seemed 
to be adherent to and be continuous with the sides of the 
abdominal cleft or laminae abdominalis. Dr. Allen Thomson, 
in the admirable account of two human embryos of this 
period, mentions that he did not perceive the amnion in 
