CHARACTERS OP SPECIES. LOCALITY. 285 



upon the most remote differences of locality. The 

 Sphinx convolvuli and the Cynthia cardui both well- 

 known British insects are likewise found in different 

 parts of Asia, and even occur in New Holland. That 

 pretty yellow butterfly, the Eurymus Electro, of the 

 south of Europe, and of Southern Africa, cannot be 

 discriminated from those found in this country. 



(345.) Individuals of a species which show any de- 

 viation from the usual characters by which that species 

 is discriminated, are called varieties. These deviations 

 from the ordinary characteristics of their race originate 

 from a variety of causes ; among which, climate, food, 

 and domestication are the most influential. In nearly 

 all cases, however, a variety is not permanent ; for, the 

 local or influential causes being removed, the generation 

 which succeeds assumes all the genuine lineaments of 

 the race from whence it originally sprang. Animals, 

 whose chief metropolis is in a temperate climate, be- 

 come smaller when they extend their limits into a 

 warmer region, and vice versa. The size of an animal 

 is greatly influenced both by the quantity and quality 

 of its food, no less than by its location ; and both these, 

 again, affect its colour. Variation in the colour of 

 quadrupeds, in a state of nature, is more rarely observed 

 than in birds ; although, in a domesticated state, the 

 former seem most disposed to deviation from the natural 

 standard. The ox, dog, and cat are familiar instances of 

 this fact ; where the diversities of colour are much more 

 remarkable than in the fowl, duck, goose, and turkey. 

 Insects of the lepidopterous and the neuropterous or- 

 ders are more prone to these variations from their 

 original type, than any other. This is observable 

 in the spots upon the wings of the Satyridce, or Argus 

 butterflies, and in the colours of the genus Agrion. The 

 testaceous shellfish, however, are sometimes very incon- 

 stant in their colours : strong instances of this are seen 

 in many species of Helix, of Oliva, and of Tellina, as 

 already intimated. 



(346.) The radiated animals are much more con- 



