EARLY ONTOGENETIC PHENOMENA IN MAMMALS, 159 
placentation will prove to be a very subtle instrument (as it 
has already shown itself to be with respect to the Primates) 
by which wide deviations in external habitat may be spanned 
and by which important generalisations may thus be 
reached.} 
Already have the voices of anatomists of different countries 
repeated what I have ventured to express more than ten 
years ago, viz. that among mammals the Primates have 
actually retained many very primitive characters. And the 
voices alluded to go even further and say that among the 
Primates the same may be said, in very many respects, con- 
cerning man as compared to the other Primates. Always 
with this one all-important reserve that his specialisation 
(a) in respect to brain development (including cerebral 
circulation) and brain power, (b) to adaptation of the fore- 
limbs to the most diverse uses, and (c) of the larynx and 
tongue to articulate speech is quite out of comparison as 
regards importance with any other series of specialisations 
that are, however, so numerous amongst the different orders 
of mammals. 
The order of the Insectivora will have to be broken up, and 
many of the small fossil mammals that may yet be brought 
to light will have to be carefully tested as to their relations 
to the different orders into which the Insectivora will be sub- 
divided. Already Wortman has proposed to transfer the 
Hyopsodidee (hitherto considered as Primates) to the In- 
sectivora. 
‘ | may here once more repeat, what I have already stated elsewhere, that 
placentation is so delicate a touchstone, because it was a phenomenon that 
appeared and evolved ever so much later than the other processes or structures 
in the vertebrate organisation, and that this comparative youth must decidedly 
contribute to retain small differences, which in older organs have been worn 
away by the effect of time. On the other hand, the details of the very early 
blastocyst must undoubtedly be of pre-eminent importance, just because they 
come to light at such a very early stage of development. ‘The different 
characteristic details of very early stages must be all-important for determining 
hereditary affinities one way or the other, as they are undoubtedly least of all 
affected by influences that call forth adaptations in the organs of the adult 
animals, 
