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ANIMALS OF EGA 



convey an adequate notion of the beauty and diversity 

 in form and colour of this class of insects in the neigh- 

 bourhood of Ega. I paid especial attention to them, 

 having found that this tribe was better adapted than 

 almost any other group of animals or plants, to furnish 

 facts in illustrations of the modifications which all species 

 undergo in nature, under changed local conditions. This 

 accidental superiority is owing partly to the simplicity 

 and distinctness of the specific characters of the insects, 

 and partly to the facility with which very copious series 

 of specimens can be collected and placed side by side for 

 comparison. The distinctness of the specific characters 

 is due probably to the fact that all the superficial signs of 

 change in the organization are exaggerated, and made 

 unusually plain, by affecting the framework, shape, and 

 colour of the wings, which, as many anatomists believe, 

 are magnified extensions of the skin around the breathing 

 orifices of the thorax of the insects. These expansions 

 are clothed with minute 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 modifications of species, so truly do all 

 changes of the organization register themselves thereon. 

 Moreover, the same colour-patterns of the wings generally 

 show, with great regularity, the degrees of blood-relation- 

 ship of the species. 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 or- 

 ganic world ; therefore, the study of butterflies — 

 creatures selected as the types of airiness and frivolity — 

 instead of being despised, 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 Amazons, 

 where the sea-breezes which blow from Para to the mouth 

 of the Rio Negro (looo 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 Amazons, from Ega upwards, and 

 the eastern slopes of the Andes, whence so large a number 



