EARLY ONTOGENETIC PHENOMENA IN MAMMALS, 167 
to Primates and Lemures, because we have concluded from 
the facts discussed in the preceding chapters that, more even 
than Huxley (’81) supposed the Insectivores to be, the 
Primates come under our consideration as containing the 
more primitive types of mammals. And it is only natural 
that they and their nearest allies will be more difficult to 
differentiate from each other than other mammals, who, even 
though archaic in some respects, were well specialised in 
others, as are many of the earlier Condylarths, Ungulates, 
and Creodonts. 
Wortman, in his remarkable discussion on the origin of the 
Primates (03, pp. 419—436) shares this opinion when he 
says: “It is true that the Insectivora furnish a type of 
cerebral circulation which might easily have passed into that 
of the Anthropoidea, through the suppression and disappear- 
ance of the stapedial branch of the ento-carotid, but, as we 
have already seen, this character is shared by the Rodentia, 
and probably by other groups as well. At the same time it 
does not form a type of cerebral circulation from which that 
of the Lemurs could have been evolved (I. c., p. 436).” 
We here havea most instructive example of that differential 
treatment of the most delicate marks visible on the base of 
the skull of fossil mammals by which their ordinal grouping 
may be influenced. And it is exactly this delicate discrimina- 
tion which I have been advocating in the preceding pages. 
The example is all the more instructive as it shows us points 
of agreement in angiological and osteological detail between 
Insectivora, Rodentia, and Primates, s. str., between which 
orders (all of them primitive) we have discussed so many 
points of comparison referring to the placenta, the blastocyst, 
etc. At the same time Wortman denies a similar degree of 
direct comparability on this particular point between Insecti- 
vores and Lemurs (see also |. c., p. 167), which, as he 
says, ‘‘are sufficiently distinct to afford reliable diagnostic 
characters.” Now we have seen that also with respect to 
their peculiar placentation (which, as I have said, is not 
necessarily as primitive as it has always been looked upon) 
