492 POPULAR SCIENCE MONTHLY 



insects to artificial heat and cold. The butterflies of the glacial regions 

 and those developed in an ice-chest have a pale coloration, and a warm 

 environment deepens the pigment. 



It has not been shown that any of these effects are hereditary, or 

 that they constitute a factor in the formation of species, although 

 climatic effects may enter into the process of natural selection. I 

 have before me a series of woodpeckers selected by a student (Mr. 

 Hubert Jenkins), which illustrates at once climatic and other sub- 

 specific variation. The collection represents the species known as 

 hairy woodpecker (Dryobates villosus). Taking the typical form 

 villosus, from the eastern United States, we note that specimens from 

 further south 1 (auduboni) are smaller in every way, but otherwise 

 similar. To the northward, in Canada and on the Arctic Sea, the 

 birds are much larger, (leucomelas) ten to eleven inches in length 

 instead of eight to nine, while the feet are scarcely if at all enlarged. 

 In all these the space before the eye is black, and the belly is darker 

 in specimens from the region having the most rainfall. In the 

 Bahamas is a form still smaller, seven to eight inches long (maynardi), 

 with the space behind the bill white. Further westward, in all wood- 

 peckers of this species, the white spots on the wing coverts, character- 

 istic of the eastern forms, nearly or quite disappear, leaving the feathers 

 plain black. Here again the northernmost forms are largest, harrisi 

 of the Californian-Alaskan region being nine to ten inches long, those 

 from California being nearly white below, those from the Vancouver 

 region smoky gray, darkest when the rainfall is greatest. The Mexican 

 form (jardini) is seven to eight inches long, but in the moist regions 

 of Central America it too becomes deep smoky brown. Of these traits, 

 those relating to the size of the bird and the smoky coloration of its 

 lower parts may probably be regarded as climatic. Whether a bird 

 born of northern parents would reach its full stature in the south, or 

 whether it would grow up with white belly plumage in a rainy district, 

 are both open to question. The experiment can hardly be tested with 

 woodpeckers, but some other group may offer conditions more favor- 

 able to artificial breeding. 



On the other hand, the loss in the western birds of the white wing 

 spots characteristic of villosus and its subspecies, leucomelas, auduboni, 

 and maynardi, can have apparently no climatic cause, but is one of the 

 results of the primitive separation of the forms on the two sides of the 

 Rocky Mountains, or more properly of the treeless plains where wood- 

 peckers of this type are not found. 



It may be noticed that in the related but much smaller American 

 species known as the downy woodpecker (Dryobates pubescens), the 

 eastern forms (pubescens) have also the wing coverts profusely spotted 

 with white, while in the western form (gairdneri) the wing coverts, as 

 in the western forms of Dryobates villosus, are nearly or quite plain 



