RIIOPALOCERA. 23 



perfect insects almost exclusively, dependent on the higher plants for 

 food. It is very noteworthy that the Butterflies met with at great 

 altitudes are of the same genera, and sometimes even of the same 

 species, as those found in the highest latitudes ; and this intimate 

 alliance of high alpine and circumpolar forms points with unmistak- 

 able significance — as in the pai'allel case in plants — to the long pre- 

 valence of the last cold period or glacial epoch.^ 



Of the five Families of Butterflies, the Nymphalidce, Lyccenidce, and 

 Papilionidce are the most widely and generally distributed ; but two 

 Sub-Families of the first of these, viz., the Ifeliconince and BrassolinoB, 

 are peculiar to Tropical America (Neotropical Region), and the Sub- 

 Family Papilionince of the third is very poorly represented in Europe 

 and temperate Asia (Palsearctic Region) and in North America. The 

 Erycinidce have one Sub-Family, the Lihyniccincc, which (though con- 

 sisting of but one genus and twelve species) ranges over the globe — 

 without penetrating, however, into the coldest parts ; but while the 

 Nemcdbiinm have a few representatives scattered about the world, the 

 great majority of them is Neotropical ; and the remaining Sub-Families, 

 Eurycjoninm and EryciniTwe, are confined to America, where but very 

 few of the latter exist north of Mexico, by far the larger part and all 

 the Earyfjoninai being limited to the tropical (chiefly Brazilian) lands. 

 The HesperidcBy although very much more generally spread than the 

 Erycinidce, still find their metropolis in the wonderfully rich Neotropi- 

 cal Region, twenty of the thirty-three genera recorded from there being 

 peculiar to it, and several of those genera containing very numerous 

 species. Two Sub-Families of the Nymiihalidcr., the Danaince and 

 Acrceinm, may also be regarded as by no means of general distribution, 

 because, although both have a very wide range of longitude, and the 

 former group sends a few stragglers into the Nearctic and Palsearctic 

 Regions, they are almost wholly tropical and sub-tropical in their ran^^e ; 

 the Danaince prevailing in the Neotropical and Oriental Regions, and 

 the Acrceinm in Africa and its islands (Ethiopian Region). 



Tropical America is undoubtedly by far the most productive region 

 for Rhopalocera. Some idea of its riches may be formed from the 

 facts that at Parii, at the mouth of the Amazons River, a year's collect- 

 ing yielded Mr. Bates about 600 species ; and that in four years, at 

 Ega, on the Upper Amazons, he obtained 550 species. Par^ has 



^ As the climate in either Northern or Southern Hemisphere grew continuously colder, it 

 seems clear — as so many able naturalists have pointed out — that there must have been a 

 gradual retreat towards the equator of animals and plants of temperate latitudes, accom- 

 panied by a simultaneous advance in the same direction of the organisms characteristic of 

 the frigid zone. The geological evidence shows how very severe cold prevailed over the 

 l)resent temperate latitudes ; and it is reasonable to suppose that, when at length gradually 

 rising temperature set in, and the organisms unfitted for a warm climate had to retreat in 

 the direction of the pole, many animals and plants existing at the base or on the foot-hills of 

 mountains would, as time went on, find their refuge at hand on the higher elevations, and 

 finally remain isolated there, while their kindred were driven to higher latitudes, and sup- 

 planted in temperate lowlands by the advancing forms from nearer the equator. 



