Blenkins, on an Early Human Ovum. 7 
either. I can readily understand^ from what I observed of 
its delicacy and transparency in this specimen, that it might 
easily be overlooked without the aid of a low magnifying 
power. Passing off from the fore part of the caudal end 
of the body is a delicate sac, containing an opaque cord- 
like substance, which can be distinctly seen through the 
membrane by transmitted light ; this is evidently the allan- 
tois, and agrees precisely with the figure and description of 
the corresponding part in the ovum examined by Wagner, 
which has been before referred to. Miiller found a similar 
structure attaching the embryo to the chorion, which he 
has described, and is of opinion that the cord was not com- 
posed of vessels, but appeared to be a simple structure. 
Coste and other observers have also given precise information 
regarding this structure. After very careful and frequent 
examination of this part in the specimen before me, I have 
come to the same conclusion, and I believe it is the remains 
of this structure which we recognise in the more advanced 
foetus under the name of the urachus. By its lower and 
broader end the allantois joins the chorion, at which point this 
opaque tubular-like part is seen suddenly to terminate. 
Velpeau, in his ^ Ovology,' states that in all the embryos 
he examined at this period, they were invariably found to be 
attached by an umbilical cord to the chorion ; as he clearly 
refers to the part which is now under consideration, it must 
be admitted to be an erroneous view to take of it, for the 
structures entering into the composition of the part which 
in the progress of development becomes the umbilical cord, 
consists, not only of the u.mbilical vessels and the remains of 
the allantoic duct or urachus, but contains as well the obli- 
terated duct or pedicle of the vitelline sac, all bound together 
by a peculiar gelatinous areolar tissue, and surrounded 
externally or inclosed in a tubular sheath derived from the 
amnion, whereas, at this early period, the amnion has 
not begun to invest any of these parts, and they are quite 
distinct. 
It is not my intention, on the present occasion, to enter 
into the question of the utility of the allantois at this stage 
of embryonic life when it is found to be most developed, or 
to inquire whether it has relation to the nutrition of the 
embryo, as supposed by Yelpeau, or receives the urinary pro- 
duction as well as conducting the foetal vessels to the chorion, 
according to most embryologists. We must first clearly 
establish which is the human embryonal structure that corre- 
sponds to the more highly developed allantois of animals, and 
this, I think, has been completely decided by the researches 
