iv CENTRES OF RADIATION 1 03 



very early types. Professor Osbom 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. 



