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Transactions of the 
portion of the vertebral column situated beyond the rudiments of 
the lower extremities and representing principally the coccyx, 
formed an appendix of such a length that it might, without any 
impropriety, and in support of Darwin's theory, well be looked 
upon as a tail. (Fig. 16.) The embryo itself was attached to the 
walls of the egg by a delicate membrane, which, after arising 
gradually from the abdominal surface, and including, but not 
closely surrounding, the umbilical vessels, was soon blended with 
the walls of the egg. (Figs. 16 and 17.) The rudimentary heart, 
alimentary canal, and umbilical vesicle, were not embraced by this 
membrane, but, laying at its right side, were projecting into the 
general cavity. 
Eeferring, for a better understanding of the general form of 
the embryo, the reader to the drawing accompanying this article, 
which I carefully took from the object in its fresh condition, while 
immersed in water, I shall now state and consider the results of the 
microscopical examination, regarding the structure of the umbilical 
vesicle and chorion of this interesting specimen of human embryo, 
as they really formed the principal object of the investigation. To 
do so, however, I must somewhat deviate from the object, in order 
to recall to our mind the structure of the umbilical vesicle, in 
which I discovered the origin of the coloured blood-corpuscles, 
described in my treatise on that subject.* It will be remembered 
that the embryo to which it belonged had been arrested in its 
growth, being represented only by an accumulation of embryonic 
cells. Further, that the wall of this vesicle was found to be a 
system of primary follicles and canals, the interior of which was 
lined by large hexagonal cells, in which the blood-corpuscles 
originated in the form of pale douljle-contoured nuclei. The interior 
of the follicles and canals were occupied by considerable accumu- 
lations of fully-developed coloured blood-corpuscles. 
The examination of the umbilical vesicle of the small normal 
embryo, described above, became therefore a matter of interest, 
as its results would either disprove or corroborate the correct- 
ness of the conclusions which I had drawn from the observa- 
tions made on the former specimen. They proved to have been 
correct, for in examining a portion of the wall in its fresh un- 
changed condition, the individual follicles with their intervening 
canals could be distinctly recognized. As in the former case, the 
follicles consisted of the same large hexagonal cells (Fig. 18), which 
also contained, besides a number of small nuclei, one or two larger 
ones. But there were no fully-developed coloured blood-corpuscles 
to be seen either within the follicles or the canals. In place of 
these, however, a considerable number of free small round nuclei, 
containing a number of granules, were observed. The same kind 
* ' M. M. J.,' February number, 1874. 
