Page:The Zoologist, 4th series, vol 6 (1902).djvu/347

Rh speedy occurrence of the chemical action which brings about the maturation of pollen and ova, we cannot neglect this factor of colour. The dusky mountain Argus, gathering radiant energy in its wings and body on a sunny slope, at the onset of an alpine storm creeps into the cover of the thick grass, where radiation from its body-surface is not so rapid as in the open air; it folds its wings above its body, and this again prevents rapid radiation from the vital regions so covered. If it be one of those Erebias—such as E. lappona or tyndarus—which are confined to the highest regions, it offers to the expanse of the outside air not the dark brown of its upper surface, but the lighter grey of the under side of its hind wings, which thus have a lower emissive power. Again, we cannot neglect the factor of colour in determining the vital capacities and functions in so far as they are influenced by temperature.

My object in these remarks has been to draw attention to some experiments by Prof. Bachmetjew on the temperature of insects; these experiments confirm the opinion that the effects of Nature are seldom brought about by causes acting singly, but by a complex interaction of many simple causes.

The surface colour of organisms must certainly be taken into account when considering their temperature relations; there appear to be suggestions in Nature that certain colours have been selected as being advantageous to the animals possessing them, owing to their absorptive, emissive, and reflecting powers; and this factor may have acted in common with many others, known and unknown, in producing the varied effects which we see and admire.