162 PROBLEMS OF GENETICS 



wild cherry (Prunus serotina) a species on which astyanax can 

 live, though that tree is not known to be eaten by arthemis. 

 Incidentally also the observations show that sterility cannot be 

 supposed to be the bar which maintains the distinctness of 

 arthemis and astyanax. 



In this connection Papilio oregonia and bairdii should be 

 mentioned. 14 P. oregonia is one of the numerous forms like 

 machaon, but rather paler. It is a northern insect, inhabiting 

 British Colombia east of the Cascade Range, and reaching to 

 Colorado. P. bairdii is a much darker butterfly, representing 

 the asterias group of the genus Papilio. Like asterias it has the 

 abdomen spotted at the sides, not banded as in the machaon 

 group. It belongs to Arizona and Utah extending into Colorado. 

 From Colorado the form brucei is described, more or less inter- 

 mediate, like bairdii but with the abdomen banded as in oregonia* 

 W. H. Edwards records the results of rearing the offspring of the 

 bairdii-\ike and of the oregonia-\ike mothers. Each was found 

 able to have offspring of both kinds, that is to say, bairdii 

 females gave both forms, and oregonia females gave both forms. 

 It is not possible to say which is dominant, since the fathers were 

 unknown. On general grounds one may expect that the bairdii 

 form will be found to dominate, but this is quite doubtful. 



From this particular discussion I omit reference to those 

 examples in which the permanently established types are ob- 

 viously associated with special conditions of life. Where con- 

 siderable climatic differences exist between localities, or when we 

 pass from South to North, or from the plains into Alpine levels 

 we often find that in correspondence with the change of climate 

 there is a change in the characteristics of a species common to 

 both. When I say "species " in such a connection I am obviously 

 using the term in the inclusive sense. Some would prefer to 

 say that in the two sets of conditions two representative species 

 exist. Whichever expression be preferred it is plain that such 

 examples present another phase of the problem we have been 

 just considering, and in them also we have an opportunity of 



14 For the facts and further references see W. H. Edwards, Butterflies of N. 

 America, 2d series, Papilio VII and X; 3d series, 1897, Papilio IV, Can. Entom. t 

 1895, XXVII, p. 239. 



