128 THE ENTOMOLOGIST. 



meteorological causes, and not dependent at all upon natural 

 selection. 



Mr. Cooke suggests that the geological formation is a 

 possible cause of variation, and I cannot say that it is not so ; 

 at the same time it requires proof. As for the occurrence of 

 pale forms on chalk and other light-coloured formations, that 

 is brought about by natural selection, not by the geological 

 formation. The range of certain species may be confined to 

 certain formations, but that is, perhaps, not due to the 

 formation itself, but to the food-plants being confined to that 

 particular formation. Still, however, plants common to various 

 formations may on one formation acquire some chemical 

 constituents that may make them, in this case only, suited to 

 be the food-plants of certain species, and hence the range of 

 the insect be restricted to that formation, though the food- 

 plant is not. In the same way the food-plants may on certain 

 soils affect the colours of the insects; but if it is so at all it 

 is probable only in a few cases. The influence of the food- 

 plant upon the colours of insects seems not to be very great, 

 though there are a few species which are theoretically 

 supposed to have become separated from other, closely 

 allied, species by modifications induced by the food-plant. 

 If my memory serves me, Eupitltecia pulchellata and 

 E. linariata are instances of this supposed influence.* 



The history of the smoky varieties of TepJirosia biundularia 

 is very interesting: they may, perhaps, be due to chemical 

 influences on the food-plants. If such is the case it ought to 

 be easy of experimental proof. (As this variety is still, I 

 believe, nameless, I take this opportunity of suggesting for it 

 the name Delamerensis. It is, of course, rather an aberration 

 than a variety, taking these terms as defined by Dr. Staudinger.) 

 This aberration and the ab. Douhledayaria (Mill.) of Amphi- 

 dasis hetularia are, however, exceptional cases, and cannot 

 be considered as throwing much light on the origin of the 

 majority of melanochroic forms. 



The latter part of Mr. Cooke's paper (though of equal or 

 greater interest) treats of a different subject, and one to which 

 1 also have paid some little attention. My investigations in 



* Since this was written some facts have preseuted themselves to me 

 which suggest the idea that Ino statices and I. Geryon may be instances of 

 modification produced bj' different food-plants. — F. B. W. 



I 



