1607 
Now against this point of view Husrecut opposed in the above 
mentioned treatise (1895) his own widely different one, which 
caused a sensation amongst the ranks of embryologists, and may 
be summarized in the following points: 
1. If the real signification of the amnion is that of a protective 
watercushion, it should originate as a closed bladder, otherwise one 
cannot understand its phylogenetic evolution. 
2. This mode of development occurs in fact in certain Mam- 
mals (Hrinaceus, Galeopithecus, Pteropus, Cavia, perhaps Primates), 
while the development by a process of folding, as most Sauropsida 
show it, differs very widely from it. Therefore it is obvious that 
the last method must be considered as a secondary one, but then 
we are obliged at the same time to derive the meroblastic yolkladen 
eggs of Sauropsida from the holoblastic yolkless eggs of Mammals 
and the (secondary) oviparity of the first group from the more 
primitive viviparity of the last one. 
3. The trophoblast i.e. the ectodermal covering of the exembryonic 
fruitbladder, to which the peripheral ectodermlayer of the embryonic 
region sometimes may be added, plays an important part in the 
formation of foetal membranes and in the implantation of the 
embryonic vesicle into the wall of the maternal genital duets. 
Husrecut considers the trophoblast as the most primitive of foetal 
membranes. In amphibian larves, especially in tadpoles, it presents 
itself as the covering ectoderm-layer (Deckschicht), in Mammals with 
deciduous placentation it develops enormously in connection with 
its intensified nutritive function. 
+. Originally the amnionbladder develops as a cavity between 
trophoblast-covering and embryonic knob. In order to secure vascula- 
risation the primitive amnion is divided by ingrowing vasoconductive 
mesoderm into. two layers: the outer chorion and the inner amnion. 
In this way the amnion cavity is separated definitively from the 
outer trophoblast-layer and can increase along with the developing 
embryo, so that in later stages it fills up the greater part of the 
fruit bladder. 
5. In some cases (most Rodentia with inversion of germlayers e.g. 
Muridae) the mesodermfolds do not penetrate the primitive amnion, 
dividing it into two layers, but grow into the primitive amnion 
cavity, and divide this cavity into the so-called false and true amnion. 
cavities. This mode of development forms a transition towards the 
folding process which appears in all Sawropsida and in many Mammals 
with postponed attachment of the embryonic vesicle In this case 
a merely ectodermal primitive amnion is never present, but the 
