264 
i; I CHARD ASSIIETOX. 
Cumulate placenta. 
Great radial proliferation of tro- 
phol^last, leading to thickening 
of the membrane. 
Greater destruction of maternal 
tissue. 
Much bleeding of mother. 
Lacunisation of trophoblast. 
Secretion of uterine glands of less 
use or in some cases of no use 
to foetus. 
Degeneration of uterine epithe- 
lium and glands severe. 
Embryo or embryos seldom fill 
the whole cavity of the uterus. 
Plicate placenta. 
Great tangential proliferation of 
trophoblast leading to folding 
of the membrane. 
Lesser destruction of maternal 
tissue. 
Little bleeding of mother. 
No lacunisation of trophoblast. 
Secretion of uterine glands of 
prime importance. 
Little or no degeneration of 
uterine epithelium and glands. 
Embryo or embryos usually fill 
the whole cavity of the uterus. 
The reason for the occurrence of the latter character being 
no doubt that fixation is brought about by imbedding or other 
iutirnate connection in the cumulate type, while fixation in the 
plicate type depends more upon the internal hydrostatic 
pressure of the blastocyst up against the uterus — much as a 
pneumatic tyre retains its position in the iron rim of a bicycle 
wheel. 
All those are essential characters and are nearly all due to 
the nature of the trophoblast and allantois, i. e. of embryo 
rather than mother. 
Modifications, especially within an order, maybe due to the 
maternal influences. Thus, whether the embryo becomes 
wholly imbedded as in the rat, with typical cumulate character, 
or approaches the plicate type as in the rabbit (though the 
trophoblast undoubtedly shows its intrinsic cumulate charac- 
ter in the beginning) depends upon absence of the albumen 
layer in the former case allowing the embryo to be caught 
ill the narrow chinks of the uterine wall and to become 
quickly parasitic, or presence of the albumen layer in the latter 
which compels the embryo to remain free for a much longer 
time before it can become parasitic. 
Or as another instance may be mentioned the presence of 
certain areas — Hubrecht’s trophospongia as in Tupaja, or the 
cotyledonary burrs of Ruminants which determine the spots 
