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- 
