DISCONTINUOUS DISTRIBUTION OF MAMMALS. 68 1 



to inspect and review only in such isolated regions as Australia 

 and Madagascar, where the process can be reconstructed with 

 more certitude. 



The orders have been established on the basis of the 

 universal possession by the members included in it, of certain 

 complexes of characters ; but I want to instance a few cases 

 for which it is possible to believe that whole complexes of 

 characters have been developed separately. 



My first case is that of the marsupials in general, of which 

 we know that they have become differentiated into forms, strik- 

 ingly similar to those of the placental mammals. And in par- 

 ticular I want to instance the marsupial mole {Notoryctes) and its 

 parallel the golden mole {Chrysochloris) of South Africa. The 

 two animals are so strikingly similar, not only in fur and general 

 appearance but also in skeletal characters, that Professor Cope 

 has insisted on the genetic affinity between them. Such an 

 afifinity, in the sense that both are descended from a common 

 ancestor of more or less similar structure is absolutely out of 

 the question, and we must conclude that the characteristic struc- 

 ture has, as a whole, been evolved twice in the two distant 

 localities. 



My second example is that of the horse. Starting from 

 the Eocene, we have in both America and in Europe a series of 

 parallel forms culminating in the Equidse in Europe and in 

 America in a horse-like creature, which, in fact, seems to have 

 been recognised as a horse in the Argentine by John Cabot in 

 1530, i.e.^ at a date apparently too early for the European horses 

 to have established themselves there. 



The series are so similar that we have either to imagine a con- 

 stant migration between the twO' continents, which is, of course, 

 not impossible, or to assume that the two series represent a case 

 of very exactly parallel evolution. 



The third case is that of the African Otocyon, which has 

 one grinder more than the Canidge are defined as possessing, and 

 has, moreover, an inflected lower jaw. Mr. Beddard* states in 

 effect, that we must either assume that this dog has gained a 

 molar (which is improbable judging from what we know of the 

 course of evolution as regards dentition) or must believe that 

 Otocyon has evolved separately from other dogs, and in doing 

 so has reproduced the true dogs in the minutest details. 



Further instances of such parallel evolution will be men- 

 tioned further on. but enough has been said to make out a case 

 in its favour, and we may now proceed to our review of the 

 Creodont-like mammals. 



The unspecialised Creodonts were animals with a full denti- 

 tion, imoerfectly ossified palate, and Ion?, powerful, orobablv 

 prehensile tails. It is, however, doubtful whether the early 

 marsupials can be separated from these Creodonts : and when 

 we bear in mind the dif^cultv at present experienced in defining 

 the living marsunials. for which purpose not onlv the skeleton 



♦"Mammalia." Camb. Nat. Hist. 



