ARACHNIDA. 119 
A striking Mammalian feature in the distribution of Scorpions is their absence from 
New Zealand. Another is to be found in the character of the Australian forms, some 
of which are quite peculiar, while others show affinity with genera and species from 
southern Asia, like the Australian Rodent Mammals, and one, like Thylacinus, belongs 
to a South American family. Again, some of the South Asiatic genera do not pass 
Wallace’s Line, and the small number of Mascarene forms are related to, but distinct 
from, those of tropical Africa and Asia, like the Mascarene Civets and Lemurs. 
Similarly, the tropical African and Asiatic species, although related, belong mostly to 
distinct genera. 
What is true of the Scorpions is true also, broadly speaking, of the two suborders of 
Pedipalpi, the Urotricha and the Amblypygi, which, like the Scorpions, existed in 
Carboniferous times in Europe and North America. The absence of both from New 
Zealand and Australia, and of the Urotricha from Africa also, are suggestive rather of 
comparatively recent origin than of high antiquity. 
The same cannot, however, be said of a great many of the Aranew (Spiders). The 
most ancient existing type, Liphistius, apparently related beyond doubt to Carboni- 
ferous genera, is restricted to Indo-Malaysia, whereas many genera, like Lycosa, 
Aranea, Tetragnatha, and others, not known to be ancient forms, are practically 
cosmopolitan in distribution. Moreover, some groups of spiders—perhaps Mesozoic or 
even Czenozoic, but not, so far as records tell us, Paleeozoic—attest by their restriction 
to the southern Continents the former existence of ‘‘ Antarctica” much more forcibly 
than the orders of Arachnida known to have been in existence in the Carboniferous 
Period. Another instance of the restricted distribution of a Carboniferous order is 
supplied by the Rianulei, which are found now only in tropical West Africa and Brazil. 
Thus some of the Carboniferous Arachnida, the Scorpions, exist in Europe, Asia, 
Africa, America, and Australia; others, the Amblypygi, in Asia, Africa, and America ; 
others, the Urotricha, in Asia and America; others, the Rianulei, in Africa and South 
America; the Mesothelid Spiders (Liphisticus) only occur in the East Indies, while 
other spiders, assumed on morphological grounds to be of later date, may be cosmo- 
politan, and such spiders, when young, are known by their method of floating on 
webs to be able to cross arms of the sea in the direction of prevalent winds *. 
From these facts it seems clear that the present distribution of the Arachnida 
depends, not upon the duration of their existence, but upon their means of dispersal 
and power of adaptation to varied conditions. Hence the attempt to explain away 
the facts of their distribution by an appeal to their antiquity is barren of results, and, 
since the paleontological history of the Arachnida throws no useful light upon the 
matter in hand, it has been ignored in the following discussion. 
* This means of dispersal is analogous to the flight of birds, whose powers to cross tracts of ocean cannot 
be ignored in discussions of geographical distribution. 
