THE DISTRIBUTION OF SPECIES. 



215 



In 1871, Dr. Joel A. Allen published his masterly 



paper on the Mammals and Winter Birds of Florida. 



This memoir has had the practical effect 



Work of Dr. f making all our ornithologists, for the 



J. A. Allen. . . . .... 



most part against their will, believers in 



the theory of derivation of species. Dr. Allen took up, 

 as a matter of serious study, the variations in individual 

 birds. He showed that the variation of individuals of 

 the same species was far greater than had been sup- 

 posed, and that the characters relied upon to distinguish 

 species were often due to slight increase in these varia- 

 tions. For example, in Northern birds the bodies would 

 be larger, the bills smaller than in birds of the same spe- 

 cies from the South, and the coloration of birds was 

 often directly related to the degree of rainfall. He 

 showed, in brief, that each one of these many variations 

 must be held to define a distinct species, or else that the 

 number of species of American birds would have to be 

 greatly reduced and the range of variation inside the 

 species would need to be correspondingly extended. 



This claim for attention on the part of the despised 

 variety produced much consternation among students of 



birds. But facts must be recognised, and 

 Species defined the fin&1 result hag bgen that w 



by missing links. , 



now extended our idea of each species 



until it is broad enough to include all that we know of 

 intermediate and varying forms. But these intermediate 

 forms must be known, not guessed at, before the status 

 of a species is questioned. When a hiatus appears, 

 whether existing either in fact or in our material for 



To the forms mentioned above Mr. Dwight adds var. adusta, 

 small and "scorched pink" in general hue, from southern Ari- 

 zona and northern Mexico ; var. menilli, large and dusky, in 

 Idaho and neighbouring regions ; and var. pallida, very small and 

 pale, from Lower California. 



