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ARACHNIDA *. 
By R. I. Pococs, F.R.S. 
INTRODUCTION. 
Discussions on the geographical distribution of the Arachnida, especially of 
Scorpions, commonly open with a reference to the great antiquity of the group, and 
to tle possibilities thus afforded it of achieving cosmopolitan dispersal. Dr. Hans 
Gadow, for instance +, dismisses the Scorpions in the following paragraph :—“ ‘This 
group is a good illustration of the effect of great antiquity. Scorpions already existed 
in the Silurian, and even some existing species date back to the Coal Measures! 
‘They have had every chance of spreading widely. A species of Tityus is preserved in 
Miocene amber of the Baltic, this genus is now restricted to southern South America. 
The group is cosmopolitan, limited only by cold, yet it is absent from New Zealand. 
They show scarcely any generic affinity between the Old World and the New, nor 
between South America and Australia. They have had sufficient time to develop 
along lines aloof from each other in these great land complexes.”’ 
Much of this is untrue both in substance and in fact. None of the many Carboni- 
ferous genera can be referred with certainty even to existing families; and the record 
of a species of “ Zttyus” from the European Miocene can only be regarded as evidence 
of the existence of the Buthide in the Baltic area in mid-Tertiary times; and, as 
regards the distribution of existing forms, if the views above expressed be accepted, 
there is nothing more to be said upon the subject. They are, however, inadmissible 
since they leave wholly unexplained the fact, singular though it be, that the present 
distribution of Scorpions does not attest the great antiquity of this order. If they 
were not known to be of Carboniferous age they might be judged, from the analogy 
supplied by Mammals, to date from late Mesozoic and early Tertiary times, for, as I 
have elsewhere pointed out {, if the surface of the world be regionally divided in 
accordance with the distribution of Scorpions, the resulting map will agree tolerably 
closely with the map based upon the distribution of Mammals, due allowance being 
made for the absence of Scorpions at the present time from all countries to the north, 
roughly speaking, of the 45th parallel of north latitude. 
* The Opiliones and the Acari have been omitted from this essay, the former because Mr. F. O. P. Cam- 
bridge was not sufficiently acquainted with them to make his results altogether reliable, and the latter 
because of the imperfection of our knowledge of the Acarine fauna of other parts of the world. 
+ ‘The Wanderings of Animals,’ 1913. 
~ ‘ Natural Science,’ iv. pp. 853-364, 1894, and 1899, pp. 213-231. 
