22O ENTOMOLOGY 



direct effects of food, light or other primary factors. Such cases, 

 then, are in a sense accidental. For example, many inconspic- 

 uous green insects are green merely because chlorophyll from 

 the food-plant tinges the blood and shows through the skin. 

 If it be argued that natural selection has brought about a thin 

 and transparent skin, it may be replied that the skin of a green 

 caterpillar is by no means exceptional in thinness or trans- 

 parency. Moreover, 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 experi- 

 mented upon by Poulton, their 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 in- 

 dividuals as were most responsive to the stimulus of the sur- 

 rounding 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 " protec- 

 tive resemblance" are very far-fetched. On the other hand, 

 when the resemblance is as specific and minutely detailed as it 

 is in the Kallima butterflies where, moreover, special instincts 

 are involved the phenomenon 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 accumulated 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 



