144 ORIGIN, ETC., OF THE FAUNA. 
that the close likeness between the Australian Scorpion Cercophonius and several 
South American genera nor the resemblances between the genera of trap-door Spiders 
referred to Migide (p. 131) are due to parallel evolution. Nor is it at all intelligible 
to me why the Scorpions and Spiders in question have disappeared entirely from all 
parts of the world except the southern continents, if at one time they were Holarctic 
in distribution. Nor can I think that raft-transportation will account for their present 
discontinuous range. Whether the land-bridge theory is the true explanation is, 
of course, quite another matter; but it appears to me to be the least improbable of 
the four *. 
* Elevations of ocean-floors to connect continents are usually regarded as vast changes. From the human 
standpoint the epithet is justifiable; but, if the diameter of the earth be taken as a standard, such changes 
raay be described as infinitesimal. 
