DUEIKG THE RECENT ARCTIC EXPEDITION. 105 



ing, a flora that must have strongly resembled that now possessed 

 by the southern portions of the United States. This k emphati- 

 cally shown in the fossil plants collected by Capt. Feilden, and 

 which are now in the hands of Prof Heer for working out. It is 

 reasonable to suppose that a parallel insect-fauna then existed. 



After this, from causes not easy to explain (and it is not neces- 

 sary here to refer to the various theories advanced in explana- 

 tion), there came a period of gradual cooling down ; and I think 

 all evidence goes to prove that this resulted in the establishment 

 of an arctic or circumpolar fauna. This was probably initiated 

 in the older Pliocene period, and culminated before tbe establish- 

 ment of the Grlacial epoch, when the mighty masses of ice began 

 to move southward, destroying animal life, or driving what re- 

 mained of it before them. Again, there came a time when an 

 increasing temperature began to manifest itself. Tbe survivors 

 of the arctic fauna commenced to move northward : a portion of 

 them settled on the tops of high mountains and established the 

 existing alpine fauna ; stragglers reached the home of their ances- 

 tors in the Arctic regions and became the progenitors of the spe- 

 cies now existing there. What is practically this theory was first 

 advanced in 1846 by Edward Porbes, in a paper " On the Geolo- 

 gical Eelations of the existing Pauna and Flora of the British 

 Isles," publisbed in vol. i. of the ' Memoirs of the Greological Sur- 

 vey of Grreat Britain.' In one form or other it has since been 

 accepted by Darwin, Lyell, Hooker, and others in England, and 

 by Packard, G-rote, and LeConte in America. How far north 

 this fauna may now extend we perhaps never shall know. Sir J. 

 D. Hooker, writing in 1860, expressed an opinion that not far 

 north of 81° would prove to be the limit of flowering plants. 

 The recent expedition found th em beyond that limit ; and if 

 the coast-line, instead of trending east and west at the highest 

 point reached, had proved to still further extend in a northerly 

 direction, 1 doubt not that both Phanerogamous plants, and also 

 insects, would have been found. 



That both alpine and arctic insects are prone to run into 

 puzzling varieties is known to every entomologist : this is stri- 

 kingly exhibited in some of the materials now under conside- 

 ration. If my idea that more than one year is often necessary 

 in these regions for an insect to undergo all its transformations 

 be correct, we have one powerful factor in explaining the causes 

 of variation ; and a still more potent one is to be found in the 



