220 CERTAIN LAWS OF VARIATION. 



species which make migrations of less magnitude." 

 This is in conformity with the rule that species inhabit- 

 ing more extensive and diversified areas show more in- 

 dividual variation than those with small or insular 

 breeding areas, and also with another rule, " that 

 species with geographical races evince a greater amount 

 of individual variation than do species which are not 

 divided into such races, provided that the breeding area 

 is approximately equal in extent and diversification in 

 both cases." Again, it was found that males generally 

 exhibit a greater amount of individual variation than 

 females of the same species, the males being most vari- 

 able in 60.4 per cent, of the 273 cases investigated, and 

 the females most variable in 39.6 per cent, of them. 



From these facts Montgomery deduces what he con- 

 siders to be a very important conclusion, viz., that " in- 

 dividual variation is greater in amount in those species 

 which we must consider under the influence of a con- 

 tinuous process of development than in those species 

 which we must consider as being influenced by no 

 process of development at all." Though this view 

 seems highly probable, yet it appears to me that the 

 data adduced do not in any way prove it. Because a 

 bird occupies an extensive breeding area, or is migra- 

 tory, it does not follow that it is undergoing develop- 

 ment either progressive or retrogressive. The only de- 

 duction which seems to me permissible is the one above 

 mentioned, one which has, indeed, been drawn by Mont- 

 gomery himself in the following words : " The amount 

 of individual variation stands in a direct ratio to the 

 degree of complexity of the environmental forces which 

 influence the organism," 



