424 EVOLUTION AND ANIMAL LIFE 



fl}dng, long-lived, and hence more exposed females, as compared 

 with the lighter, swifter, short-lived males. 



It has been found that individuals of a single species may 

 mimic several different species of defended insects, this poly- 

 morphism of pattern existing in different localities, or indeed 

 in a single one. Marshall believes that seasonal polychromat- 

 ism of certain butterfly species is associated with the mimicry 

 of certain defended butterflies of different species, these different 

 species appearing at different times of the j^ear. 



It is needless to say that such hypotheses and theories of 

 the utility of color and pattern have been subjected to much 

 criticism, both adverse and favorable. The necessity for limiting 

 results within the working range of efficient causes has been 

 the soundest basis, in our judgment, for the adverse criticism 

 of the theories of special protective resemblance, warning 

 colors, and mimicry. Until recently most of the observations 

 on which the theories are based have been simph^ observations 

 proving the existence of remarkable similarities in appearance or 

 equally striking contrasts and bizarrerie. The usefulness of 

 these similarities and contrasts had been deduced logically, 

 but not proved experimentally nor by direct observation. In 

 recent years, however, a much sounder basis for these theories 

 has been laid by experimental work. There is now on record 

 a large amount of strong evidence for the validity of the hypoth- 

 esis of mimicry. Certainly no other hypothesis of equal 

 validity with that of protective resemblance and mimicry has 

 been proposed to explain the numerous striking cases of similar- 

 ity and the significant conditions of life accompanying the ex- 

 istence of these cases, which have been recorded as the result 

 of much laborious and indefatigable study by certain naturalists. 



Plateau and Wheeler have tasted so-called inedible and 

 distasteful insects and found nothing particularly disagreeable 

 about them. But as Poulton suggests, the question is not as 

 to the palate of Plateau and Wheeler nor of any man; it concerns 

 the taste of birds, lizards, etc. Better evidence is that afforded 

 by actual observation of feeding birds and lizards; of experi- 

 mental offering under natural conditions of alleged distasteful 

 insects to their natural enemies. Marshall's observations and 

 experiments on the point are suggestive and undoubtedly 

 reliable. Much more work of the same kind is needed. 



The efficient cause for bringing color and pattern up to such 



