24 



. We now come to atmospheric influences, and here we find thafrr 

 in degrees of temperature acting upon the chrysaUs, we possess- 

 the most powerful agent yet discovered to produce variation ; but 

 before discussing this, let us dispose of the other atmospheria 

 conditions which tend fo modify the perfect insect. 



Easterly wind will sometimes delay the appearance of an insect 

 until long after its proper time for emergence, perhaps compelling, 

 it to lie over for another year, and thus indirectly, by prolonging- 

 the chrysalis state, be the cause of variation, for it is well known 

 that certain chrysalids, especially those who have fed internally, as- 

 caterpillars, will wriggle themselves towards daylight, with the 

 intention of coming out, and then, having had a taste of a north- 

 easter, alter their minds and beat a hasty retreat. 



Eain or humidity v/ould seem to operate on the insect about to 

 emerge. By moisture we try to account for the darlyiess of some 

 species taken in the West of England, Ireland, and the Isle of 

 Man, because it cannot be accounted for by cold, as in the case of 

 Scotch butterflies and moths. We know that if moisture gets 

 between the scales, displacing the air, the colour is altered, and a 

 curious enquiry into the cause of the green of the underside of a 

 green hair streak turning red when wetted, has lately taken place. 



Electricity is supposed to be a cause of variation amongst the 

 blues, more particularly those which emerge during a thunderstorm,, 

 these being of a beautiful lilac instead of the ordinary blue colour,, 

 but it is just possible that the enriching of the colour is due to the 

 oppressive heat which generally precedes a summer storm, and we- 

 shall see further on that one of the effects of heat is to convert blue 

 into violet owing to the formation of red pigment. Mr. Sydney 

 Webb, however, says that tortoiseshell butterflies which emerge 

 before a storm are paler, while those appearing after it are darker. 

 (Examples exhibited by Mr. Sydney Webb.) 



The French have suggested an apparatus for subjecting chrysalids. 

 to the effects of an artificial storm by isolating them in a little^ 

 sulphur cell and placing them between the electrodes of a battery 

 to represent an electrical condition of atmosphere, and also effecting 

 occasional discharges to represent lightening, but the results have 

 been negative, and the insects which emerged did not seem any the 

 worse for this treatment. 



Heat and Cold. — A good many years ago some notes in the 

 French Annals, especially one by M. Bellier, de la Chavignerie^^. 

 written in .1858, attracted my attention. M. Bellier's note ran. 

 thus: " One day a friend of mine brought me several tortoiseshell 

 butterflies, which, owing to the wings being excessively dark, and 

 adorned with large, intensely black spots, immediately excited mjr 

 admiration. He assured me that these remarkable specimens hacL 



