526 The American Naturalist. . [June, 
temperature and humidity, are dominant powers in geograph- 
ic distribution), the most potent of which is temperature; 
fourth, that the predominating distribution of the respective 
colors is largely confined to the faunal divisions of the East- 
ern United States, and as such is approaching the sub-specific 
differentiation of the two phases; lastly, that the Darwinian 
theory of ‘Reproduction with variation and the survival of 
the fittest,’ is well exemplified in our common little Megascops 
0. 
The Screech Owl has been made the subject of investigation 
simply because it offers one of the best known examples of 
dichromatism : if explained and disposed of in one case, much 
light will be thrown upon the same problem relating to many 
forms of animal life. 
To begin with, a short description of the young, together 
with the manner of attaining the adult plumage of both 
phases, may be of service to many not thoroughly acquainted 
with the species. When first hatched they are covered with. 
pure white down, which in a week or ten days begins to show 
faint traces of transverse dusky bars.. At the age of four 
weeks they are fully barred with gray and white alternately, 
which markings they retain until the appearance of the first 
full plumage. As a usual thing, those destined to be red 
assume a rufous cast in the down shortly before the appear- 
ance of the feathers, but this is not always the case, as 
instances are known where the first intimation of red was the 
appearance of a rufous feather pushing its way through the 
gray or mottled down. Such instances, however, are rare, and 
but few are known to the writer. At the period when feathers 
first appear, the future color of the young bird is settled 
beyond a doubt; both the gray and the red birds rapidly 
attain their mantle, and the colors once assumed are never 
changed. Much confusion has arisen from the fact that some 
observers apparently make no distinction between the bird in 
the gray or mottled down and the gray or mottled plumage 
and upon the appearance of the red feathers through the gray 
down, the assertion has been made that the gray feathers 
changed to red.. The gray birds, on the other hand, attain 
