EARLY ONTOGENETIC PHENOMENA IN MAMMALS. 89 
maternal mucosa in the region where the placenta will later 
appear is most precocious and elaborate, are decidedly in the 
first case. 
And still there is here no free allantois at all, We must 
consequently try to analyse whether the method, according 
to which the vascularisation of the trophoblast comes about 
in the Primates, points in the direction of secondary changes 
by which the formation of a free allantois was precociously 
forestalled, or whether, on the contrary, the phenomena are 
such-as to make it probable that the vascularisation is here 
brought about in a yet simpler, more direct, and more 
primitive way. In the latter case comparison with those 
mammals that possess a free allantois is none the less neces- 
sary, but then we may expect to meet a free allantois in its 
earliest incipient stages, only in the Primate stem in 
geological periods so far back that we can safely say that it 
will never actually reveal itself to us. ‘These Primates, 
reaching back into the mesozoic and paleeozoic epochs, had 
evidently better be called Proprimates, or even Protetrapods. 
As soon as a free allantois arose a step was taken in the 
direction of one of the numerous sidebranches: Sauropsida, 
Ornithodelphia, Monodelphia, etc. 
At the same time we will then have to look out for transi- 
tion forms which may serve to explain how, out of the 
more primitive arrangements of the Primates the free 
allantois of other mammals, and of the Sauropsida has come 
to evolve. 
Now of the Primates that have no free allantois, man and 
the monkeys have not yet furnished a material of sufficient 
extension to study the very early stages of their vascular attach- 
ment in detail. For this we have to fall back upon Tarsius, 
which I have been able to investigate on this point (702) in 
sufficient numbers to enable us to emit a constructive hypo- 
thesis with respect to what is called the ‘ Haftstiel” or 
“ Bauchstiel,” i.e. the connective stalk by which the embryo 
communicates with the vascularised trophoblast, without 
any free allantois having preceded it. 
