126 YORKSHIRE NATURALISTS' UNION. 



although the actual amount of sunshine in the arctic and sub- 

 arctic regions is infinitely less than in latitudes more nearly 

 approaching the equator, the length of daylight is considerably 

 greater during the summer months. In the absence of actual 

 frost a varying amount of absorption would still be in progress, 

 even when the sun had ceased to shine, and this could not fail 

 to have its effect in cases where the vital energy of the insect 

 was not dependent upon direct solar rays. Captain Feilden 

 records that during the short period when there is practically 

 no night, butterflies are continuously on the wing, supposing 

 the sun's face to be not obscured by clouds or passing snow 

 showers.* 



The chemistry of colour in living organisms is a subject 

 which has been but little studied. 



The researches of Dr. Sorby, one of my distinguished pre- 

 decessors in your presidential chair, will be still fresh in your 

 memory. I am indebted to his kindness for enabling me to 

 refer to several of his valuable papers published in various 

 scientific journals. He discovered the presence of several 

 interesting substances in the colouring matter of shells, egg 

 shells, t and human hair. | His experiments would certainly 

 favour the conclusion that although radiation and absorption 

 alike involve motion, changes of colour due to external circum- 

 stances acting upon living organisms are dependent upon 

 chemical rather than upon strictly mechanical action. 



This is supported by Newport's discovery § that insects 

 possess the greatest amount of natural heat at the moment when 

 their wings are just dried and hardened. Finding that respira- 

 tion increased and diminished in the same degree as temperature 



* Mac Lachlan, Journal of Linnean Society, xiv, p. 103. 



t Proceedings of Zoological Society, 1875, p. 351. 



+ Journal of Anthropological Institute, 1878, p. i. 



§ Philosophical Transactions R. S., vol. 127, p. 259, et seq. 



Trans. Y.N. U., 1883 (pub. 1885). Series D 



