88 A. A. W. HUBRECHT. 
to spread out against that portion of the blastocyst-wall, 
where the placenta is going to be formed. Thus in mammals 
the allantois was both anatomically and physiologically the 
homologue of what was designated by that name in Saurop- 
sida. 
One difficulty was this, that in man no free allantois was 
ever detected, the (involuntary!) attempt of a German 
embryologist to let a chick-embryo stand for an early human 
foetus, only serving—once the fraud detected—to emphasize 
the existing difficulty. Moreover, further investigations 
showed that in no monkey, and not either in Tarsius spec- 
trum was any free allantois present. 
It seems to me that the confusion even now yet rampant 
concerning the phylogeny of the allantois would not have 
arisen if evolutionary principles had been more logically 
adhered to in the attempts to trace that phylogeny. 
Observation shows that the main significance of the 
allantois in the developmental history of the higher verte- 
brates is a nutritive one, thanks to the strong vascularisation 
of its walls and the close contact into which these are brought 
either with vessels of the maternal mucosa (many Ungulates, 
Lemurs, and others) or with blood-spaces in the trophoblast, 
to which maternal blood gains admittance, thanks to the 
transitory arrangements furnished by the trophospongia 
(most other placental mammals). 
Vascularisation of the diplotrophoblast or of the chorion 
(as I have proposed [’96, ’99] to continue calling the outer 
embryonic envelope only in Primates) is thus the outcome of 
the developmental phenomena noticed in what has been 
called the allantois. And there is reason to believe that such 
mammals as have attained this aim most completely and at 
the earliest moment will be safer guides for teaching us how 
the arrangement may have come about phylogenetically than 
those in which the appearance of this vascularisation is for 
one reason or another retarded. 
Now the Primates, who have no trace of omphaloidean 
placentation, but whose trophoblastic attachment to the 
a“tyg 
