30 
AN EARLY HUMAN OVUM 
Figure 18, with Peters’ Figures 1 and 22). Leopold’s ovum further resembles 
Peters’ more closely, (1) in having two kinds of cells in the trophoblastic 
processes, and (2) in the characters of the mesoblast. The principal 
difference between the two is that the trophoblastic processes are more 
numerous and much thicker in Peters’ ovum, so that, as compared with 
Leopold’s specimen, the blood lacunae are much reduced in size, and the 
trophoblast takes the form of a thick layer containing blood spaces. The 
attachment of the primitive villi to the decidua appears to be very similar 
in both cases, but the degree of intermingling is much greater in Peters’ 
ovum, and the condition of the decidua is also different. Whereas in 
Leopold’s ovum (see his Figures 23 and 24) the zone of decidua next the 
trophoblast is largely in the state of coagulation necrosis, characteristic of 
the present specimen, in Peters’ case the decidua has a much more living 
appearance; there is more mingling of living cellular elements, and the 
amount of necrotic material visible is relatively small. There is evidence 
of active reaction on the part of the decidua in Peters’ case, as shown 
by the presence of large numbers of polymorphonuclear leucocytes and 
formation of new vessels; this is less marked in Leopold’s case, but the 
invasion of leucocytes is very striking in the present specimen. All three 
ova however show a very distinct reaction as far as dilatation of blood¬ 
vessels is concerned, and this is greatly exaggerated in Leopold’s case by 
congestion which is probably due to the mode of death. 
In respect therefore of the trophoblast the ovum of Leopold may with 
some confidence be considered as a stage intermediate between the present 
ovum and that of Peters’; but as there was no embryonic rudiment the 
comparison cannot be carried further. 
When the embryonic rudiment in the present case is compared with 
that in Peters’ blastocyst, it is at once apparent, that if our interpretations 
be correct, this ovum is at a considerably earlier stage of development. 
THE EMBRYONIC RUDIMENT. 
It will be necessary to explain at this point the data on which our 
interpretation of the embryonic rudiment is based. 
