1616 
Now if the germbladder remained free in the uterine cavity 
the growing embryo would soon evolve the original entypy, 
a phenomenon which is realized in some Mammals (e.g. in Tupaja) 
under somewhat altered conditions. When however osmotic inter- 
change between maternal and foetal blood has been settled, it is 
plausible that the embryo tries to profit from this relation as much as 
possible, and that foetal and maternal bloodvessels approach each 
other very closely. Trophoblast-outgrowths therefore attack the 
mucous membrane of the uterine wall, penetrate into the latter and 
pierce the wall of the maternal vessels so as to fill up the gaps 
and cavities of the trophoblast with maternal blood. The corrosion 
will chiefly take place at the embryonic pole of the germbladder 
i.e. at the spot of the original entypy since in this manner the 
connection between foetal and maternal circulation by way of the 
connective stalk becomes as intimate as possible. The maternal 
tissue will answer to this attack of the foetal vesicle by overgrow- 
ing it in all directions, enveloping it totally in order to avoid 
bleeding to death. Now in the attached fruitbladder, totally enveloped 
by maternal tissue there cannot be question of evolving the original 
entypy. 
We may imagine the original entypy as a hollow invagination 
and may then call the cavity with Resink archamnion-cavity and 
its wall archamnion. On the other hand no serious objection can 
be made to imagining the stalk which pushes the embryonic knob 
into the trophoblastvesicle to be originally solid. In the first case 
the archamnion cavity will pass continually into the definitive am- 
nioneavity. The ectodermal archamnion will become separated from 
the trophoblast by ingrowing mesodermfolds as 1 have already men- 
tioned in explaining Husrecut’s theory. This happens in most 
Rodents with so called inversion of germlayers. In the second case 
the amnion cavity arises by delamination in the tissue of the solid 
amnionstalk and forms from the beginning a closed waterbladder 
above the embryonic region. This manner of development, occurring 
in Wrinaceus, Galeopithecus, Pteropus, Cavia and perhaps in Primates’), 
has heen the starting point of HuBrrcurt’s theoretical considerations. 
I hope to have made it clear that in my opinion this difference is 
1) The occurrence of the so called tubes of Selenka in Primates (ResiNK, Lc. 
p.179; H. Srrant und R. BeNEcKE. Ein junger menschlicher Embryo. Wiesbaden 
1910; ©. Grosser. Über hypothetische Frühstadien menschlicher Entwicklung. 
Zentralbl. Phys. Bd. XXII, 1908) which may be considered as remains of an 
open archamnion-cavity, makes it doubtful whether they do not belong to the 
first group. 
