EHOPALOCEEA. 
23 
perfect insects almost exclusively, dependent on tlie 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 parallel case in plants — to the long pre- 
valence of the last cold period or glacial epoch.-^ 
Of the five Families of Butterflies, the Nymphalidm, Lyccenidce^ and 
Papilionidce are the most widely and generally distributed ; but two 
Sub-Families of the first of these, viz., the Heliconince and Brassolince, 
are peculiar to Tropical America (Neotropical Eegion), and the Sub- 
Family Papilioiiince of the third is very poorly represented in Europe 
and temperate Asia (Palaearctic Region) and in North America. The 
ErycinidcB have one Sub-Family, the Libythminmy 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 
NemeoMince have a few representatives scattered about the world, the 
great majority of them is Neotropical ; and the remaining Sub-Families, 
Eurygoninm and Erycinince^ are confined to America, where but very 
few of the latter exist north of Mexico, by far the larger part and all 
the Eicrygonince being limited to the tropical (chiefly Brazilian) lands. 
The Hesperidce.j 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 Nymphalidce, the Danainm and 
Acrceince, 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 range ; 
the Banaince prevailing in the Neotropical and Oriental Regions, and 
the Acroeince 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 Para, 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 
present 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. 
