266 STUDIES, SCIENTIFIC AND SOCIAL ch. xii 



of opposing coasts, would greatly facilitate the migration 

 and accidental transmission of individuals. 



Another point of great importance to which attention is 

 called in Mr. Murray's essay, is the long-persisting identity 

 of form which seems to be a characteristic of insects, and 

 which is thought to allow ample time for those revolutions 

 in geography to which he so constantly appeals. But this 

 antiquity and persistence of insect-forms will have allowed 

 equal time for the action of a most powerful agent of dis- 

 tribution, which is too hastily dismissed. I allude to those 

 changes of climate, which within a period so recent as the 

 Miocene, have at one time clothed the now inhospitable 

 regions of North Greenland, Spitzbergen and other Arctic 

 lands, with forests and evergreens and flowering shrubs, 

 and at another have covered the Northern United States 

 and Central Europe with a mantle of ice like that which 

 at present envelopes Greenland. These vast climatic 

 changes must have afforded ample facilities for insect 

 migrations, — between the eastern and western hemispheres, 

 when the arctic regions were inhabited by a temperate 

 flora and fauna, — between the northern and the southern, 

 when the animals and plants of either hemisphere were 

 driven towards the Equator by the glaciation of their native 

 regions, and when a portion would cross that barrier, either 

 along the elevated lands or by transmission over narrow 

 seas. This cause is admitted by our best botanists to be 

 amply sufficient to account for the presence of European 

 genera and species of plants on the Andes, in Chili, 

 Patagonia and Terra del Fuego, in New Zealand, and in 

 the Australian Alps. The relations of South America, 

 Australia, and other southern lands to each other, are still 

 more marked, and probably more deep-seated, and seem to 

 imply either a greater extension or the existence of inter- 

 mediate lands at some former period, but not an actual 

 continuity with one another. 



I believe that the curious and suggestive facts which I 

 have disinterred from that bulky and little-read volume, 

 the Inseda Maderensia, may be of some use to students of 

 the geographical distribution of animals. 



