THE GEOGRAPHICAL DISTRIBUTION OF AXTS. H7 



seek for antecedent explanatory conditions in geology and paleontology. 

 In ethological studies, on the other hand, one turns at once to the 

 adaptations of the living forms to their specific environment and works 

 hack from these adaptations to the geographical and geological con- 

 ditions by which they are influenced. Of these two methods, which 

 necessarily supplement each other, the latter leads to more detailed and 

 positive results, since our knowledge of previous faunas is in all cases 

 more or less vague and problematic. A resume of what has been ascer- 

 tained concerning fossil ants will be given in the next chapter, but 

 owing to its fragmentary character, will be used rather as a confirma- 

 tion than as a foundation for inferences drawn from our existing fauna. 

 Emery (1893- '94) and von Ihering (1894) have shown that there is 

 a very significant parallelism between the distribution of mammals and 

 that of ants. Both groups appear to have arisen simultaneously dur- 

 ing the Triassic or possibly during some previous period, and to have 

 spread over the earth's surface in much the same manner, although, 

 if we except the bats, few mammals have possessed such power of dis- 

 persal as the ants. A study of the mammals indicates that during the 

 Mesozoicera there were extensive land connections between the present 

 continents of Eurasia, Africa, America and Australia, and that these 

 various regions were inhabited by a primitive, widely-distributed but 

 now extinct fauna. During this era Xew Zealand was cut off from 

 Australia and during the following Eocene epoch Africa, South Amer- 

 ica and Australia were in turn separated from the great continental 

 mass. During the Oligocene a boreal and Indian fauna became differ- 

 entiated in Eurasia and their separation was emphasized during the 

 Miocene and Pliocene periods by an upheaval of the boundaries between 

 the respective regions. During the early Tertiary, also, the connection 

 between Xorth and South America was severed and was not restored, 

 according to some paleontologists, till the Pliocene epoch. It is highly 

 probable, as Emery has suggested, that the Ponerin?e correspond to 

 the primitive, widely-distributed mammals of the Mesozoic era, and 

 together with certain Myrmicinae, like Solcnopsis, Phcidole, etc., rep- 

 resent an ancient cosmopolitan ant-fauna. Ponerinae occur even in 

 Xew Zealand, which appears to have been isolated ever since the 

 Jurassic. Since the Dorylinse are well developed in the tropics of 

 both hemispheres, these ants must have arisen before Africa was sepa- 

 rated from South America, probably from some primitive and wide- 

 spread Ponerine forms like the Cerapachysii. The almost complete 

 absence of Dolichoderinse in Africa shows that this subfamily must 

 have made its appearance after Africa had been separated from Eurasia. 

 That the Dolichoderinae came from Ponerine ancestors is indicated 



