94 MAMMALIAN DENTITION 



shaped in the Koala, lophodont in the Kangaroos and columnar 

 in the Wombat. 



Parallelism is exhibited in the evolution of the molars of 

 Dendrolagus and Macropus. These two Kangaroos are related 

 ancestrally in the primitive bunodont stage alone but because 

 of the inherent tendency of animal types to respond morpho- 

 logically in the same manner to the same environment and life 

 habits the lophodont dentition is strikingly similar in both. 



The last mentioned principle gives some clue to the forma- 

 tion of species and genus. It is possible that a new species is 

 finally evolved through similar and simultaneous modification 

 of numerous individuals although the part played by muta- 

 tions appearing in a single individual should not be underesti- 

 mated. It is claimed that a new genus of South American fresh 

 water fishes is even now in process of development through the 

 transformation of several species of an older genus, the change 

 going on simultaneously but independently in widely separated 

 parts of the continent. 



