X] MIMICRY AND VARIATION 133 



pigment in the wings may depend in some degree upon 

 the nature of the food. The larvae of D. chrysippus 

 feed upon various Asclepiads, and it is at any rate 

 conceivable that the pigment formation, and con- 

 sequently the details of pattern, may be in slight 

 measure affected by the plant species upon which they 

 have fed. The species of food plants are more Ukely 

 to be different at the extremities of the range of a 

 widely distributed form Hke D. chrysippus, and if they 

 are really a factor in the pattern it is at the extremities 

 that we should expect to find the most distinct forms ^. 

 Actually we do find this in D. chrysippus, though it 

 does not, of course, foUow that the cause suggested is 

 the true one, or, if true, the only one. Of the nature 

 of local races too little at present is known to enable 

 us to lay down any generahzation. We must first 

 learn by experiment how far they remain constant 

 when transported from their own environment and 

 bred in the environment under which another distinct 

 local race is hving. The behaviour of the transported 

 race under the altered conditions would help us in 

 deciding whether any variation by which it is character- 

 ised had a definite hereditary basis or was merely a 

 fluctuation dependent upon something in the conditions 

 under which it had grown up. The decision as to 

 whether it is hereditary or not must depend upon the 



1 The size of the white spot may shew much variation in specimens 

 from the same region. I have seen African specimens in which it is 

 large, while in the Ceylon specimen figured on Plate IV it is as small as 

 in the typical African specimen shewn on Plate VIII. 



