OF THE Sl'liEAD OK THE ECKOPEAN' FAUNA. 



Ill 



and inanv beetles, of v.iiich there are altocjether no less than 

 100.000 species. 



The two remarkable species of Orthoptera (2fantis rdigiosa), 

 the Praying Insect,and the Stick Insect {Bacillus) must be added. 

 There are also a few spiders and a notable crustacean, the f resh- 

 vrater crab {Thclphusa fluviatilis), which in Europe is quite 

 contined to the south. 



Arctic Immigrants. 



Although in the early Glacial period much of Northern 

 Europe was submerged below the Glacial sea, yet there seems 

 to have been continuous land extending from the Arctic regions 

 southwards by the Scandinavian highlands to Scotland and 

 England, and so to Central Continental Europe, for the Straits 

 of Dover were not then cut through. By this long and narrow 

 land communication, animals miglit travel southwards as the 

 rigors of the Glacial period increased in the more nortlierly 

 lands. At the same time, with the extension of the Arctic land 

 westwards to Greenland and Xorth America, species inhabiting 

 those remote Xorthern lands could find a way to Europe. 



Tims can be accounted for the existence in the British Islands 

 of animals from both Arctic and Xorth American habitats. 

 Some of these doubtless migrated from Xorth America to 

 Greenland and the Earoe Islands in still earlier times, probably 

 later Tertiary, and then afterwards proceeded southwards when 

 glacial conditions impelled a further migration. 



Arctic conditions may include a great variation of tempera- 

 ture, one period being much more tolerable for animal life 

 than another. Of this there are abundant evidences not rnly 

 in the Arctic remains of animals, but much more in the Arctic 

 fossil plants. But however much temperature may liave 

 changed, the shortness of winter days and lengthened 

 nights, with short summers without darkness, have l>een 

 constant accompaniments of Polar regions, and so climatal 

 influences have always played a great part in determining tlie 

 fauna of far Xorthern lands. The remarkable prevalence of 

 white as the winter colour of both mammals and birds of 

 Arctic lands is a conspicuous testimony to the powerful effects 

 of the conditions of high latitudes. 



As has been pointed out by Dr. Scharff, the large number of 

 Lepidoptera, 24o species, found by Moschler to be common to 

 both Xorth America and Europe, and tliat twelve species while 

 common to Xearctic and Pahearctic lands are absent from 



