04 THE ENTOMOLOGIST. 



have one nearly suffused with black, Pkisia festuccB is here 

 of a rich dark colour ; in Glen Spean it is much lighter ; and 

 I could go on enumerating these differences in coloration, 

 but I have instanced enough for my purpose. Neither 

 sexual selection nor the survival of the fittest larvae account 

 for melanic variation. We must look for other causes. 



The most interesting case of melanism that has come under 

 my observation — and my friend Mr, N. Greening, of War- 

 rington, can say if I exaggerate the facts — is the total change 

 in the colour of Tephrosia hUmdularia,m Delaraere Forest. 

 Some thirty years since, when he and I visited Petty Pool 

 Wood, this species was very abundant, appearing in March, 

 and was to be found through April and May, but all were of 

 a creamy white ground colour; dark varieties were so scarce 

 that they were considered a great prize. Now, it is just the 

 reverse; all are dark, smoky brown, approaching black; a 

 light variety is very rare. The same change, and nearly to 

 the same extent as regards numbers, has come over Amphi- 

 dasis hetularia throughout the district, from Petty Pool, 

 including Warrington, to Manchester; the black form is now 

 usually found. I am inclined to suspect that climate and 

 manufactures have done more to bring about this change 

 than anything else. During the past thirty years what large 

 towns have sprung up to the west of this district! Runcorn, 

 Widnes, St. Helens, Earlstown, Wigan, &c., all pouring forth 

 from their tall chimneys chemical fumes and coal smoke, 

 which emanations are carried over our collecting grounds by 

 every westerly wind ; and the wind is westerly for nine months 

 out of the twelve. This may have effected a change in the 

 climate, as well as deposited on the leaves of trees and 

 food-plants of Lepidoptera matter which may possibly 

 cause some white insects to become gradually black, through 

 being swallowed by the larvae along with their food. 



Electricity may have something to do with causing curious 

 varieties occasionally, but I question very much its having 

 any influence in creating such a change as that which has 

 taken place in the colour of T. hiundularia. It is also 

 likely, I think, that geological formation influences colour in 

 insects; for we find species on chalk and limestone of light 

 colour, and dark species more prevalent on other formations; 

 but there does not seem to be any law even here, for the 



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