l'J2 THE CANADIAN ENTOMOLOGIST. 



offered proof to show that among the British lepidoptera the darkest forms 

 are commonest in the more humid parts of England. Given an excitant 

 cause, he shows that as moisture in the atmosphere tends to darken the 

 soil, trees and other natural objects, natural selection would, if not inter- 

 fered with by opposing forces, tend to perpetuate the melanic forms. This 

 line of thought has suggested to me the desirability of making some 

 inquiries regarding the climatic conditions of the different regions from 

 which my own specimens come. A request for figures stating average 

 annual precipitation has at once been acceded to by Prof. Mark. W. 

 Harrington, Chief of the U. S. Weather Bureau, who has kindly sent me 

 the appended statistics : — 



Annual precipitation at Albuquerque, New Mex. 

 " " Helena, Montana, 



" " Flagstaff, Arizona, 



" " Prescott, Arizona, 



In most of these cases the observations have extended over a number 

 of years, but the recoid for Flagstaff, Ariz , has been kept for only seven- 

 teen months, and Prof. Harrington writes me that it may be too high an 

 average. My object in getting the figures for the months of May to 

 October (inclusive) is this : If the action of mo'sture on the colours of 

 insects be purely physiological, it would act chiefly, no doubt, while the 

 insect was growing, — that is, through the active part of the larval stage, 

 extending through the warmer months of the year ; if, on the other hand, 

 it acts indirectly by bringing the tints of the insect, through the work of 

 natural selection, more closely in harmony with the darker colours with 

 which this wet weather would surround it, it must nevertheless act during 

 these same months. 



While my paper does not deal exclusively with any one species, those 

 treated of are closely allied, and on this ground it may prove profitable to 

 make a few comparisons. 



Fifty specimens of C. loiigipennis from the driest of these points — 

 Albuquerque, New Mexico — show thirty-two males, none of which have 

 more than a very slender line of black along the suture, and eighteen 

 females, most of them coloured like //, several as light as k, and only one 

 as dark as /;. C. tcstaceus, from the dry regions of Southern California, 

 is also notable from its lack of black markings. I found C. longipennis 

 abundant upon golden-rods (Solidago), which had a very solid head of 



