ON THE HISTOliV OF THE SPREAD OF THE EUROPEAN FA IN A. 103 



French savants, and tlie writings and lectures of Dr. Scliarff", 

 uf])ublin, who has trained for it wide rccoL?nition.* 



The word fauna is used in science to inchide not only all 

 forms of living animal organisms, the lowest as well as the 

 highest, but also all animal organisms that have lived in patt 

 geological epochs, Paleozoic as well as Neozoic, l^ut in this 

 paper reference will necessarily be omitted to tlie lowest 

 invertebrates, and to Man, the highest vertebiate, as well as to 

 the vast number of species that have ceased to iidiabit this part 

 of the earth's surface before the Quaternary epoch. 



In approaching the question of whence and by what routes 

 came the animals of Europe, it is in the first place necessary to 

 know their present habitats and dispersal, by wliicli knowledge 

 may be obtained some indication of the direction of their 

 original homes. It is also requisite to know the proportion of 

 species in many localities, that the region inhabited by the 

 maximum number may be determined. Consideration must 

 likewise be given to the causes that produce, facilitate, retard 

 or hinder migration, both biologically and geographically. 



The enquiry into geographical and climatal conditions, as well 

 as of configuration both of land and sea, and of surface elevations 

 and depressions, opens up the great (]uestion of the changes of 

 land and sea areas, and of great alterations of temperature 

 which have taken place in recent geological times: but for our 

 particular and limited enquiry, the changes that hav(^ taken 

 place in the Eurasian area, or, more precisely, in the I\\la'arctic 

 region of Dr. Sclater will be sufficient. 



These geographical changes having been produced by geological 

 causes, and followed by geological results, can only be known 

 by the study of the geology of the region affected, and the 

 conclusions derived therefrom. This, ot course, affords scop3 

 for much disputation as to details, but the general conclusions 

 may be said to be well established. 



The importance of geographical changes in determining the 

 course of a migration of animals is obvious, since wide sea areas 

 render impossible the passage of all vertebrates except: birds, 

 and of all invertebrates except some insects. The change there- 

 fore of a land area into a sea area, or of a trca area into a land 

 area, will have most important distributional conseipiences. The 

 elevation of land, too, is a powerful iuHuence, since it is followed 

 by a lowering of tenqierature, and if the elevation is great, 



* A review by the Secretary of Dr. Scliarfi"'rf lectures, in book form, 

 will appear in the succeeding, volume of Traiisactions, No. XL. 



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