Royal Microscopical Society. 
15 
of nuclei I found within the cavity of the rudimentary heart and 
also within the newly-formed blood-vessels of the chorion. (Fig. 19.) 
In examining the chorion I found it to consist of an amorphous, 
granular membrane, covered by an epithelium, consisting of a 
decidedly granular matrix, in which a considerable number of small 
nuclei were imbedded; the villi consisted of the same elements. 
Within the structureless membrane of the chorion I observed, to my 
astonishment, a considerable number of the smaller blood-vessels and 
capillaries (Fig. 19), some of them far enough developed to allow 
the circulation of the blood, others still in process of development. 
They, however, extended not into the villi. As their structure 
showed, they had been formed by the fusion of spindle-shaped 
bodies. A number of those small granular nuclei, above mentioned, 
were met with in their interior. A considerable number of oval 
nuclei were distributed throughout the membrane, occupying the 
meshes of the capillaries. Some of these latter nuclei I discovered 
in the act of multiplication, not by the process of budding, how- 
ever, as in the chorion of the abnormal embryo, described in the 
first pages of this article, but, on the contrary, by that of direct 
division. 
In reviewing now the different facts, regarding both the mode 
of origin of the blood- corpuscles within the follicles of the umbilical 
vesicle, as well as the development of the earliest embryonic blood- 
vessels in the chorion, elicited by the above examinations, and 
comparing them with those observed in the same parts of that ab- 
normal embryo, some discrepancies existing between them will 
become apparent, and it would almost seem as if my former observa- 
tions had been incorrect. But this is not the case, and for this reason 
we will give an explanation of the probable cause of these discre- 
pancies, consisting firstly in the presence of granular nuclei within 
the follicles of the umbilical vesicle and in the blood-vessels of the 
chorion of the normal embryo, instead of fully-developed coloured 
blood-corpuscles, as were met with in those organs of the abnormal, 
undeveloped embryo ; and secondly, in the mode of development of 
the embryonic blood-vessels. 
In comparing the diameters of the two ova, we shall see at once, 
that while the former abnormal one measured 2|- ctm. in diameter, 
the size of the latter normal one only amounted to about half of 
this, that is, 13 mm. in length to 11 in breadth. It becomes evi- 
dent, therefore, that the abnormal one, containing the undeveloped 
embryo, must have been considerably older than the latter. The 
structure of the umbilical vesicles of the two ova being found to be 
the same, we must presume that the fully-developed blood-corpus- 
cles found within the follicles of the umbilical vesicle of the older 
ovum, had, at an earlier time, likewise been represented by granular 
nuclei as in the other case, and by a gradual continuous develop- 
VOL. XIII. c 
