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 
of making all our ornithologists, for the 
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 
the final result has been that we have 
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 
Work of Dr. 
J. A. Allen. 
Species defined 
by missing links. 
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. meniili, large and dusky, in 
Idaho and neighbouring regions ; and var. pallida, very small and 
pale, from Lower California. 
