DISTRIBUTION 375 



Holarctic, Neotropical, Ethiopian, Oriental and Australian 



(PI- 3)- 



The Holarctic realm comprises the whole of Europe, North- 

 ern Africa as far south as the Sahara, Asia down to the Hima- 

 layas, and North America down to Mexico. Though the 

 faunae of all these areas are fundamentally alike (as Merriam 

 and other authorities maintain), it is often convenient to 

 divide the Holarctic into two parts : the Palcearctic, including 

 Europe and most of temperate Asia, being limited roughly by 

 the Tropic of Cancer ; and the Nearctic, occupying almost the 

 entire continent of North America, including Greenland. The 

 northern portion of the Holarctic realm forms a circumpolar 

 belt with a remarkable homogeneous fauna and flora ; there- 

 fore some authors distinguish an Arctic realm, limited by the 

 isotherm of 32, which marks very closely the tree-limit. 



The boreal insects of Eurasia and North America are strik- 

 ingly alike. Dr. Hamilton has catalogued nearly six hundred 

 species of beetles as being holarctic in distribution; five hun- 

 dred of these are common to Europe, Asia and North America, 

 and the remainder are known to occur in North America 'and 

 also in Europe or Asia ; one hundred are cosmopolitan or sub- 

 cosmopolitan, to be sure, but fifty of these are probably hol- 

 arctic in origin, for example Dermestes lardarius and Tene- 

 brio molitor. Of butterflies, out of some two hundred and 

 fifty species that are found in the United States east of the 

 Rocky Mountains, scarcely more than a dozen occur also in 

 the old world. North of the United States, however, as 

 Scudder finds, no less than thirteen genera are represented in 

 the old world by the same or by allied species. 



The Neotropical realm embraces South America, Central 

 America, the West Indies and the coasts of Mexico ; Mexico 

 being for the most part a transition tract between the Neo- 

 tropical and the Nearctic. The richest butterfly fauna in the 

 world is found in tropical South America. To this region are 

 restricted, almost without exception, the Euplceinse and 

 Lemoniinse and over ninety-nine per cent, of the Libytheinse; 



