1V CENTRES OF RADIATION 103 
very early types. Professor Osborn has argued that from this 
early Eutherian stock there were two waves of progress, or, as he 
expresses it, “two great centres of functional radiation.” ! 
The first was largely ineffective, the second has produced all 
the Eutherian orders of to-day. These two divisions are termed 
by him “ Mesoplacentalia” and “ Cenoplacentalia.”. The first 
division embraces the Amblypoda and their descendants the 
Coryphodonts and Dinocerata, many of the Condylarthra, the 
bulk of the Creodonts and the Tillodonts. These creatures 
persisted for a time, but died out in the Miocene. They were 
mainly distinguished by the smallness of their brain; the great 
specialisation of structure which they exhibit having left that 
organ unaffected, and therefore tending in the long run to render 
them unable to cope with changes in the inorganic and organic 
world. The successful division of the primitive Eutheria com- 
prises the groups which exist at the present day, and is not 
connected directly with those small-brained Mesoplacentals ; it 
has apparently originated, however, from the least specialised of 
their ancestors. Professor Osborn thinks,moreover, that the Lemurs 
and the Insectivores are persistent descendants of the earlier 
wave of Eutherian life. It appears in fact as if Nature had 
created the existing Ungulate, Unguiculate, and other types on a 
defective plan, and, instead of mending them to suit more 
modern requirements, had evolved an entirely new set of 
similarly-organised types from some of the more ancient and 
plastic forms remaining over. The Marsupials may be the only 
group of the early wave remaining, and they have been able to 
hold their own for the geological reason that Australia was 
early cut off from communication with the rest of the world. 
That they are disappearing seems to be shown by their gradual 
diminution as we pass from Australia towards the continent of 
Asia, through the islands of the Malay Archipelago. Com- 
petition has here decimated them, as it may do in the remote 
future in Australia. 
It is often said, but with some looseness of statement, that 
ancient quadrupeds are huger than their modern representatives. 
This statement is partly true in fact, but largely wrong in 
implication. For it suggests that—and the suggestion is often 
expressed in books that are not authoritative—huge animals 
1 Trans. New York Acad. Sci. xiii. 1894, p. 234. 
