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 Ujjper 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 



