Distribution of Peripatus 335 



explain exchanges which we know to have repeatedly taken place 

 between America and Europe, but they are not proved thereby, since 

 most of these exchanges can almost as easily have occurred across 

 the polar regions, and others still more easily by repeated junction of 

 Siberia with Alaska. 



Let us now describe a hypothetical case based on the supposition 

 of connecting bridges. Not to work in a circle, we select an important 

 group which has not served as a basis for the reconstruction of 

 bridges ; and it must be a group which we feel justified in assuming 

 to be old enough to have availed itself of ancient land-connections. 



The occurrence of one species of Peripatus in the whole of Aus- 

 tralia, Tasmania and New Zealand (the latter being joined to Australia 

 by way of New Britain in Cretaceous times but not later) puts the 

 genus back into this epoch, no unsatisfactory assumption to the 

 morphologist. The apparent absence of Peripatus in Madagascar 

 indicates that it did not come from the east into Africa, that it was 

 neither Afro-Indian, nor Afro-Australian ; nor can it have started in 

 South America. We therefore assume as its creative centre Australia 

 or Malaya in the Cretaceous epoch, whence its occurrence in Sumatra, 

 Malay Peninsula, New Britain, New Zealand and Australia is easily 

 explained. Then extension across Antarctica to Patagonia and Chile, 

 whence it could spread into the rest of South America as this 

 became consolidated in early Tertiary times. For getting to the 

 Antilles and into Mexico it would have to wait until the Miocene, 

 but long before that time it could arrive in Africa, there surviving as 

 a Congolese and a Cape species. This story is unsupported by a 

 single fossil. Peripatus may have been "sub-universal" all over 

 greater Gondwana land in Carboniferous times, and then its absence 

 from Madagascar would be difficult to explain, but the migrations 

 suggested above amount to little considering that the distance 

 from Tasmania to South America could be covered in far less time 

 than that represented by the whole of the Eocene epoch alone. 



There is yet another field, essentially the domain of geographical 

 distribution, the cultivation of which promises fair to throw much 

 light upon Nature's way of making species. This is the study of the 

 organisms with regard to their environment. Instead of revealing- 

 pedigrees or of showing how and when the creatures got to a 

 certain locality, it investigates how they behaved to meet the ever 

 changing conditions of their habitats. There is a facies, characteristic 

 of, and often peculiar to, the fauna of tropical moist forests, another 

 of deserts, of high mountains, of underground life and so forth ; 

 these same facies are stamped upon whole associations of animals and 

 plants, although these may be and in widely separated countries 

 generally are drawn from totally different families of their respec- 



