Ixviii 



a deep-seated original identity, or merely the effect of a super- 

 ficial and comparatively recent immigration ? JNIr. Murray holds 

 the former view; most botanists and almost all zoologists the 

 latter. 



Another point of great importance to which attention is called 

 in this 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 Mr. 

 Murray 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 distribution, which is too hastily dis- 

 missed. 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. And it is now becoming almost 

 certain that these changes did not occur once only, but were 

 repeated again and again far back into geologic time ; and that, in 

 the southern hemisphere, they were equally if not more strongly 

 contrasted, the glaciation of a considerable portion of Brazil 

 seeming to be a well-established fact.* 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, Avhen the animals and plants of 

 either hemisphere were driven towards the equator by the glacia- 

 tion 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 ; and Mr. Murray has hardly attempted to show that it will 

 not also account for the somewhat more remarkable distribution 

 of Microtypal Coleoptera. The relations of South America, 

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



* See Eeview of Hartt's Geology of Erazil in ' Nature,' Oct. 27tb, 1870. 



