STUDIES IN MAMMALIAN EMBRYOLOGY, 297 
areas nutritory processes could be said to be established, 
the serous membrane playing a more passive part, until the 
vascular allantois came into close connection with it, and a 
true chorion was established. We will see that our general 
conception of the process requires a careful revision, because 
.1n such primitive Monodelphia as are the hedgehogs : 
(1) peculiar nutritory facilities are already offered to the 
idermic blastocyst before the formation of either of those two 
vascular areas ; 
(2) the serous envelope (as a double layer of epiblast and 
splanchnic mesoblast, which arises simultaneously with the 
formation of the amnion) does not as such take any important 
part in the preparation of the said facilities ; 
(3) the outer cell layer of the didermic blastocyst very 
actively contributes to bring them about ; 
(4) the further part played by that epiblastic cell-layer 
alone in extending and perfecting the nutritory facilities, 
both in the omphaloidean and in the allantoidean regions is 
much more extensive and important than was hitherto ever 
expected. 
These points will all be duly developed in the further course 
of this memoir. If I here recapitulate them it is to demon- 
strate the desirableness of introducing certain new names into 
mammalian embryology. Those new names must be partly 
applied to embryonic, partly to maternal tissue, partly to both, 
when in the later stages of foetal nutrition they have come to 
be blended together very intimately. I have with especial care 
tried to select this nomenclature in a way that excludes mis- 
understanding and at the same time allows of application to 
other mammals than Erinaceus. I have tried to evade an 
undue overburdening of the nomenclature with new terms, on 
the principle introduced by Haeckel in naming new genera, viz. 
by using a common prefix for such formations as are in close 
connection with each other, independently whether they are of 
foetal or of maternal origin. ‘Thus the terms trophoblast, 
diplotrophoblast, trophospongia, trophosphere, &c., are suc- 
cessively used and explained in this paper, and the reader 
