176 THE THEOEY OF EVOLUTION 



to the evidence of palaeontology in each group, are 

 not yet so specially constituted, but show in jaw and 

 other equipment a more general character. It is this 

 circumstance precisely which enables them to nourish 

 themselves in various ways and to live in various regions 

 and habitats. Marked specialization for instance in 

 the jaw and organs of locomotion or with respect to 

 the habitat will consequently be best considered as 

 really subsequently acquired ' adaptive ' characters. 



In Australia which, as a continent, in contrast 

 with the small marine islets, presented opportunities 

 for the most diverse modes of existence the Marsupials 

 have, therefore, it is concluded, assumed the most diverse 

 forms to fit them. Since, however, they remained 

 Marsupials, therefore this example shows that they 

 present a real type which only varies but is not aban- 

 doned. If therefore which cannot be exactly proved 

 the present forms of the Australian Marsupials have 

 really developed themselves by differentiation, then 

 they form at the same time a fine proof that certain 

 basal forms are firmly retained. Time and opportu- 

 nity for the full development of their entire evolutional 

 capacity the Marsupials have certainly had, but other 

 orders they have not produced. The same thing we 

 must assume also for Europe and America if we will be 

 logical, although the pakeontological evidence in favour 

 of a genetic connection of definite mammalian groups 

 with each other is lacking. 



On other continents like North America and Asia, 

 together with Northern Europe, which for a very long 



