198 ENTOMOLOGY 



pillar is by no means exceptional in thinness or transparency. More- 

 over, many leaf-mining caterpillars are green, simply because their food 

 is green; for, living as they do within the tissues of leaves and surrounded 

 by chlorophyll, their own green color is of no advantage, but is merely 

 incidental. 



Again, in the "protectively" colored chrysalides experimented upon 

 by Poulton, the color was directly influenced by the prevailing color 

 of the light that surrounded the larva during the last few days before 

 pupation. Of course, it is conceivable that natural selection may have 

 preserved such individuals as were most responsive to the stimulus of 

 the surrounding light; nevertheless the fact remains that these resem- 

 blances do not demand such an explanation, which is, in other words, 

 superfluous. 



Indeed, a great many of the assumed examples of "protective re- 

 semblance" are very far-fetched. On the other hand, when the re- 

 semblance is as specific and minutely detailed as it is in the Kallima 

 butterflies where, moreover, special instincts are involved the phe- 

 nomenon can scarcely be due to chance; the direct and uncombined 

 action of such factors as food or light is no longer sufficient to explain 

 the facts although these and other factors are undoubtedly important 

 in a primary, or fundamental, way. Here natural selection becomes 

 useful, as enabling us to understand how original variations of structure 

 and instinct in favorable directions may have been preserved and ac- 

 cumulated until an extraordinary degree of adaptation has been attained. 



Value of Protective Resemblance. The popular opinion as to 

 the efficiency of protective resemblances is undoubtedly an exaggerated 

 one, owing mainly to the false assumption that the senses of the lower 

 animals are co-extensive in range with our own. As a matter of fact, 

 birds detect insects with a facility far superior to that of man, and 

 destroy them by the wholesale, in spite of protective coloration. Thus, 

 as Judd has ascertained, no fewer than three hundred species of birds 

 feed upon protectively colored grasshoppers, which they destroy in 

 immense numbers, and more than twenty species prey upon the twig- 

 like geometrid larvae ; while the weevils that look like particles of soil, 

 and the green-striped caterpillars thai: assimilate with the surrounding 

 foliage are constantly to be found in the stomachs of birds. 



After all, however, protective resemblance may be regarded as ad- 

 vantageous upon the whole, even if it is ineffectual in thousands of in- 

 stances. An adaptation may be successful even if it does fall short of 

 perfection; and it should be borne in mind that the evolution of protect- 



