146 MENDELISM CHAP. 



A. echeria arose suddenly from A. dominicanus (or vice 

 versa), and similarly mima arose suddenly from wahlbergi. 

 If mima occurred where A. echeria was common and A. 

 dominicanus was rare, its resemblance to the more plenti- 

 ful distasteful form would give it the advantage over wahl- 

 bergi and allow it to establish itself in place of the latter. 

 On the modern Darwinian view natural selection gradually 

 shapes wahlbergi into the mima form owing to the pres- 

 ence of A . echeria ; on the Mendelian view natural selec- 

 tion merely conserves the. mima form when once it has 

 arisen. Now this case of mimicry is one of especial in- 

 terest, because we have experimental evidence that the 

 relation between mima and wahlbergi is a simple Men- 

 delian one, though at present it is uncertain which is the 

 dominant and which the recessive form. The two have 

 been proved to occur in families bred from the same 

 female without the occurrence of any intermediates, and 

 the fact that the two segregate cleanly is strong evidence 

 in favour of the Mendelian view. On this view the gen- 

 era Amauris and Euralia contain a similar set of pattern 

 factors, and the conditions, whatever they may be, 

 which bring about mutation in the former lead to the 

 production of a similar mutation in the latter. Of the 

 different forms of Euralia produced in any region that 

 one has the best chance of survival, through the opera- 

 tion of natural selection, which resembles the most plen- 

 tiful Amauris form. Mimetic resemblance is a true phe- 



