3806 A. A. W. HUBRECHT. 
same stage that is pictured for the omphaloidean trophoblast in 
fig. 43. Generally the stretched condition of the cellular 
elements which clothe the roof of the cavity above the ger- 
minal area—the cavity in which the somatic amnion folds bend 
upwards, and for which Selenka’s designation of ‘‘ Markam- 
nionhdhle ” would not be unfit—hardly permits to identify 
them with their morphological equivalents in the region of the 
area vasculosa. 
Starting from the stages of figs. 51 and 52, the histological 
changes that occur in the allantoidean trophoblast are seen to 
evolve quite gradually in the same way as it wasjust described 
for the omphaloidean trophoblast. Fig. 53 illustrates this, and 
if we compare fig. 52 with fig. 53 it will be seen that in the 
latter figure there is still the innermost thin layer of flattened 
somatic mesoblast cells, which in fig. 52 had just given up its 
connection with the mesoblast of the amnion. Between this 
somatic mesoblast and the maternal elements, 77s., there is, 
however, a layer, 7., of more considerable thickness than the 
villiferous cell layer of figs. 51 and 52. I have no doubt in 
assigning a purely embryonic origin to this comparatively 
thick layer, Jr. It is seen to be derived from the layer Tr. in 
the preceding stage. Here again the phenomenon is one of 
growth and proliferation, both of the villi of the trophoblast 
and of the trophoblastic tissue between these. This has assumed 
a loose, more or less spongy or arachnoideal aspect. Maternal 
blood circulates in it, as was the case in the foregoing stages, but 
in addition to the spacious lacunee that are present between the 
trophoblastic villi of fig. 52, numerous secondary cavities and 
additional blood-spaces have made their appearance, and are, 
as those of fig. 52, in direct communication with the maternal 
vessels. 
A very distinct stratified layer of flattened cells (s /.) is here 
present, as in the omphaloidean region between the trophoblast 
and the maternal tissue. Before the allantois is far enough 
advanced in development to come into contact with this highly 
sanguiniferous trophoblastic tissue, the latter is seen to show 
another feature which may be said to prepare close intermix- 
