CONVERGENCE IN EVOLUTION = 257 
by themselves apart from other mammals. Now, 
it seems at first sight very remarkable that the 
marsupials should, in the course of time, have 
come to present what may be called superficial 
_duplicates of several orders of the higher mammals. 
The Tasmanian wolf converges towards a true wolf, 
the banded ant-eater to a true ant-eater, the flying 
phalanger to a flying squirrel, the swimming yapock 
to an otter, the bandicoots to rats, the marsupial 
mole to a true mole, and so on, The parallelism is 
very interesting, for marsupials are not on the same 
line as placental mammals; yet one is perhaps 
inclined to make too much of it. It must be remem- 
bered that the different kinds of habitat and the 
different ways of getting a livelihood that are open 
to mammals are not very numerous, and that Nature 
was therefore almost bound to repeat herself. In 
the same way it is not surprising that there should 
have been terrestrial, aquatic, and aerial reptiles 
in Mesozoic ages, just as there are terrestrial, 
aquatic, and aerial mammals to-day. Some good 
cases of convergence occur between rodents and 
insectivores, ¢.g., between mouse and shrew, porcu- 
pine and hedgehog, squirrel and tree-shrew; but 
we have given illustrations enough. The climax 
is to be found in the “mimicry” of unrelated types, 
but this problem is better kept apart, since the 
superficial resemblance in itself is here of survival- 
value and may be the direct result of natural 
selection. 
In his Creative Evolution Professor Bergson dealt 
