MUTATION 177 



spicuous on the grass they were relatively unfit 

 io survive, and so they were eliminated. Again 

 the elevation of the tail feathers by the hen is 

 essential to successful coupling with the male; 

 but this is impossible in rumpless hens, and they 

 must all be infertile except for an operation. 

 The wingless cock could successfully couple only 

 with bantam hens, as without wings he could not 

 balance himself while treading larger hens. 

 These examples suffice to show how unadaptive 

 mutations tend quickly to be eliminated. On 

 the other hand, the split spur, the extra toe, the 

 varied forms of comb, the frizzled and silky 

 forms of plumage, even the absence of the oil- 

 gland seem, under the conditions of the poultry 

 yard, to offer no important impediment to sur- 

 vival and propagation. We may conclude, con- 

 sequently, that selection will act on mutations as 

 well as on graduated variations, eliminating the 

 unfit and letting survive favorable mutations or 

 such as are merely neutral. But, granted that • 

 the unfit mutations are eliminated, can such a 

 case of close adaptation as is exhibited by the 

 leaf butterflies (Kallima and the rest) result from 

 a series of mutations? Does not the very per- 

 fection of the adaptation indicate that the final 

 touches have been of the quantitative order? 

 Not at all. The perfection of the result may be 

 due to a combination of adaptive unit characters. 

 Bateson,.who examined thirty-eight individuals 

 from one locality, finds that they fall into four 



