II] BATESIAN AND MULLERIAN 11 



and in future leave such butterflies severely alone. 

 The more conspicuous the pattern the more readily 

 would it be noticed by the enemy, and so it would 

 be of advantage to the Ithomiine to possess as striking 

 a pattern as possible. Those butterflies shewing a 

 tendency to a more conspicuous pattern would be 

 more immune to the attacks of birds and so would 

 have a better chance of leaving progeny than those 

 with a less conspicuous pattern. In this way vari- 

 ations in the direction of greater conspicuousness would 

 be accumulated gradually by natural selection, and 

 so would be built up in the Ithomiine the striking 

 warning coloration by which it advertises its disagree- 

 able properties. Such is the first step in the making 

 of a mimicry case — the building up through natural 

 selection of a conspicuous pattern in an unpalatable 

 species by means of which it is enabled to advertise its 

 disagreeable properties effectively and thereby secure 

 immunity from the attacks of enemies which are able 

 to appreciate the advertisement. Such patterns and 

 colours are said to be of a "warning" nature. The 

 existence of an unpalatable model in considerable 

 numbers is the first step in the production of a mimetic 

 resemblance through the agency of natural selection. 



We come back now to our Pierine which must 

 be assumed to shew the general characters and color- 

 ation of the family of whites to which they belong 

 (cf. PL X, fig. 1). Theoretically they are not specially 

 protected by nauseous properties from enemies and 

 hence their conspicuous white coloration renders 



