MEMOIR. Xxxi 
just cited Bates goes on to show that, where no great variety of 
elevation or natural barriers exist, minor climatic conditions in- 
fluence the fauna and flora of a country in their effect on soil, which 
in its turn affects vegetable and animal life. He remarks that the 
distribution of the species of Papzlzo (cne of the lowest families 
of butterflies) affords strong ground for considering the Guiana 
region as possessing productions of peculiar character, and a “ very 
large proportion of species peculiar to itself; the numerous local 
sub-specics peculiar to the Amazons all showing themselves to be 
local modifications of Guiana species,” so that Guiana is probably 
“the great centre whence radiated the species which now people the 
low land on its borders.”* Then he discusses the more abstruse 
question of Geographical Distribution, and gives reasons for dissent- 
ing from the current theories of an extension of the Glacial Epoch 
to equatorial regions,t whereby many species of temperate zones 
would be enabled to pass from the northern to the southern 
hemisphere :— 
‘‘It is supposed that at that time the climate of the equatorial plains 
resembled what now exists at six or seven thousand feet of elevation near the 
equator. It is a tolerably well-established fact that arctic forms then moved 
twenty-five. degrees southward from their homes, and if the decreased 
temperature then extended to the centre of the tropics, the regions near the 
equator must have possessed a temperature similar to what is now enjoyed 
in countries near the twenty-fifth parallel of latitude. Extinction in this case 
must have been at work largely amongst the forms (if there were any) 
peculiar to the equatorial zone, and the present character of its fauna ought 
to show, in consequence, a poverty in endemic forms, and unmistakable signs, 
in the shape of local varieties or representative species, of a dependence, on 
the part of the now existing forms, on those living towards the twenty-fifth 
parallel of latitude ; because, with the returning warmth, the extra-tropical 
species then living near the equator would retreat north and south to their 
former homes, leaving some of their congeners, slowly modified subsequently 
by the altered local conditions, to re-people the zone they had forsaken. The 
present distribution of the species of agz/z0 does not support the hypothesis 
of such a degree of refrigeration in the equatorial zone of America, or, at 
least, does not countenance the supposition of any considerable amount of 
extinction.{ The fauna of the Guiana-Amazonian region, so far as regards 
this genus, is in the highest degree peculiar; showing no dependence on that 
of the countries near either ofthe tropics. If now we except the local varieties 
(the inclusion of which would only strengthen the position), there are about 
* See infra, pp. XxXxv., 54. 
} See zzfra, p. lxxxi. 
t “There is no proof whatever of glaciation in any part of Brazil.”—Wallace’s 
Darwinism, p. 370. 
