Xo. tm] 



FOOD-PLAXTS AXD IX SECTS 



329 



strange plant (where they could be induced to select it) 

 give rise to moths whose progeny more readily accept 

 the new plant. It is very difficult to accept such evi- 

 dence, at least as having any general application, with- 

 out very clear and incontrovertible proof. If such trans- 

 formations can occur so easily and become hereditary so 

 quickly they should have entirely destroyed the coherent 

 habits now existent, during the enormous period which 

 has elapsed, for example, since the violent-feeding Ar- 

 gynnids were differentiated, since the holarctic and nearc- 

 tic Vanessids have been separated, or while the world- 

 wide Aristolochia-feeding Papilios were attaining their 

 present distribution. That such a change has actually 

 occurred in the case of other groups seems equally evi- 

 dent, although, as has been shown, we can more easily 

 believe that they may have arisen through mutations in 

 maternal instinct not incompatible with larval tastes and 

 then only in extremely rare cases and confined to certain 

 groups. 



With a knowledge of the specificity of proteins in dif- 

 ferent living organisms and their apparent differentia- 

 tion as a replica of the genealogical history of the animal 

 and plant kingdoms, has come the suggestion that the 

 dependence of monophagous or oligophagous insects 

 upon specific plants rests upon a physiological basis, and 

 that particular proteins or vitamines are an actual neces- 

 sity for growth and development. A survey of the field 

 does not seem to bear out this supposition, however 

 plausible it may appear at first sight. With monopha- 

 gous larvae, it will serve as a reasonable explanation, and 

 with oligophagous ones also so far as the individual spe- 

 cies are concerned, especially where such species select a 

 series of related plants. With those that select only a 

 few plants, however, and at the same time such as are 

 evidently not closely related, it does not seem so appro- 

 priate. It is when we compare the lists of food-plants of 

 several oligophagous species that it appears to fail com- 

 pletely to meet the requirements. Thus we find, referring 

 again to our North American butterflies, such combina- 



