No. 531] NOTES AND LITERATURE 



L91 



account," that lizards "certainly do not appear to exercise that 

 nice discrimination with regard to butterflies which is necessary 

 for the establishment of mimicking Conns on the theory of nat- 

 ural selection." and that asilids are not averse to preying upon 

 "distasteful species." 



After pointing out that the resemblances on which the theory 

 was based are far less striking in living, moving specimens than 

 in their expanded museum state, he says 



Apart then from the questions whether the resemblances in many 

 cases of mimicry are sufficiently close to he of effective service to the 

 mimic, and whether the action of natural selection can be regarded as 

 sufficiently stringent to have brought these resemblances into being, 

 there are still the following difficulties in the way of the acceptance of 

 the hypothesis of those who look to natural selection as an explanation 

 of polymorphic forms in Lepidoptera : 



1. The attribution of selection value to minute variation. 



2. The absence of transitional forms. 



3. The frequent absence of mimicry in the male sex. 



4. The inability to offer an explanation of polymorphism, where the 

 polymorphic forms can not be regarded as mimics of a distasteful 



Moreover, the hypothesis assumes that minute variations of all sorts 

 proof. a P ° Slh0n Whieh at 1 1P 18 ** 8 P 



The gist of the constructive part of his paper is as follows: 

 Natural selection plays no part in the formation of these polymorphic 

 forms, but they are regarded as having arisen by sudden mutation, and 

 series of transitional forms do not exist because such series are not 

 biologically possible. Polymorphic forms may arise and may persist, 

 provided that they are not harmful to the species, and it is possible 

 to look upon their existence as due to the absence of natural selection 

 rather than to the operation of this factor. . . . That polymorphism 

 in a species should so frequently be confined to the female sex has long 

 been remarked upon by those who study these matters, and the explana- 

 tion most favored is that the female, burdened as she is with the next 



repel the factor for some other character for which the female is also 



