346 
ANIMALS OF EGA. 
Chap. V. 
feathers or scales, coloured in regular patterns, which 
vary in accordance with the slightest change in the 
conditions to which the species are exposed. It may 
be said, therefore, that on these expanded membranes 
.Nature writes, as on a tablet, the story of the modifica- 
tions of species, so truly do all changes of the organisa- 
tion register themselves thereon. Moreover, the same 
colour-patterns of the wings generally show, with great 
regularity, the degrees of blood-relationship of the spe- 
cies. As the laws of Nature must be the same for all 
beings, the conclusions furnished by this group of insects 
must be applicable to the whole organic world ; there- 
fore, the study of butterflies — creatures selected as the 
types of airiness and frivolity — instead of being de- 
spised, will some day be valued as one of the most 
important branches of Biological science. 
I have mentioned, in a former chapter, the general 
sultry condition of the atmosphere on the Upper Ama- 
zons, where the sea-breezes which blow from Para to 
the mouth of the Rio Negro (1000 miles up stream) 
are unknown. This simple difference of meteorological 
conditions would hardly be thought to determine what 
genera of butterflies should inhabit each region, yet it 
does so in a very decisive manner. The Upper Ama- 
zons, from Ega upwards, and the eastern slopes of the 
Andes, whence so large a number of the most richly- 
coloured species of this tribe have been received in 
Europe, owe the most ornamental part of their insect 
population to the absence of strong and regular winds. 
Nineteen of the most handsome genera of Ega, con- 
taining altogether about 100 species, are either entirely 
