132 MIMICRY AND VARIATION [ch. 



evolutionary change. Before any given variation can 

 be claimed as a possible stage in the development 

 of a mimetic likeness satisfactory evidence must be 

 forthcoming that it is not of this nature, but that it 

 is transmissible and independent of climatic and 

 other conditions. 



Many species of butterflies, especially such as are 

 found over a wide range, exhibit minor varieties which 

 are characteristic of given localities. These minor 

 varieties may be quite small. In Danais chrysippus, 

 for example, African and Asiatic specimens can gener- 

 ally be distinguished. On examples from India a 

 small spot is seen just below the bar on the fore wing 

 and on the inner side of it. Eastwards towards China 

 this spot tends to become larger and confluent with 

 the white bar, giving rise to an L-shaped marking; 

 westwards in Africa the spot tends to disappear al- 

 together. The existence of such local races has been 

 used as an argument for the hereditary transmission of 

 very small variations — in the present instance the size 

 of a small white spot 1 . For if it can be supposed that 

 small differences of this nature are always transmitted, 

 it becomes less difficult to imagine that a mimetic 

 resemblance has been brought about by a long series 

 of very small steps. But before this can be admitted 

 it is necessary to shew by experiment that the size 

 of this spot is independent of environmental conditions, 

 both climatic and other. Apart from temperature and 

 moisture it is not improbable that the formation of 



1 Cf. Poulton, Bedrock, Oct. 19)3, p. 300. 



