Royal Mieroseopical Society. 
3 
chorion, however, showed the formation of the smaller blood-vessels 
not to take place, as I had observed in the former cases, by the 
coalescence of certain round cells, but by the fusion of spindle- 
shaped bodies. From this apparent discrepancy, observed in the 
formative process of the smaller blood-vessels of the chorion of these 
two different ova, it must, however, not be inferred that my former 
observations were incorrect, but we must rather seek for an explana- 
tion elsewhere. For this reason, too, I shall in the following pages 
confine myself to an accurate statement of the phenomena I observed, 
from which the reader may draw his own deductions. 
In returning now to the first ovum, containing the imperfect 
embryo, we shall commence our statements with a description of 
the structure of its wall. This consisted of two membranes, an 
outer and stronger one, the so-called chorion, giving origin to the 
villi, and an inner one, consisting of an exceedingly delicate loose 
fibrous tissue. The outer surface of the chorion, including its villi, 
was covered by a comparatively thick layer of primary epithelial 
cells or nuclei, imbedded in a granular matrix. In removing this 
layer, it was found that its base, the membrane itself (Fig. 1), con- 
sisted of an amorphous finely granular substance, in which, however, 
a considerable number of fine granular fibrillse were crossing each 
other in various directions. These represented the elementary form 
of the later fibrous or connective tissue. A considerable number of 
certain forms of nuclei and also cells were imbedded in the mem- 
brane. The most interesting of these elements were a considerable 
number of nuclei, distinguished by bearing on their surfaces concave 
depressions, corresponding to the segment of a sphere, either empty 
or occupied by double-contoured vesicles or cells (Figs. 1 and 3). 
They remind us of those mother-blood corpuscles, described in the 
paper before mentioned, having, as will be remembered, similar 
depressions on their surfaces, which, however, differed in this 
respect, as they were produced by the separation of a consistent, 
though soft body (the embryo blood-corpuscle), in the case of the 
nuclei in question, they were caused by the separation of a small 
vesicle, arising from the substance of the nucleus ; in other words : 
in the one case, the product was an embryo blood-corpuscle, while 
in the other it was a vesicle or cell, destined, as we shall see, to take 
part in the formation of the primary embryonic blood-vessels, or to 
develop, perhaps, into a nucleus itself. The process of multiphca- 
tion of the nuclei and cell, therefore, instead of consisting in a 
division of the old, we find here to take place by a separation of the 
young brood in the form of a vesicle or bud, being in reality a 
process of ludding or gemmation. The whole process takes place as 
follows : on the surface of the nucleus, and partially imbedded in its 
substance, a small globular body appears, which, gradually enlarging, 
is developed into a clear double-contoured cell. This may either 
