568 THE AMERICAN NATURALIST. [VOL XXXII. 
smallest, in almost exact proportions. It was evident, then, that 
the female had laid the eggs at regular intervals, and very likely 
three or four days apart, and that incubation commenced imme- 
diately after the first egg was deposited. What is more worthy 
of note, however, is the fact that the sexes of these nestlings 
aN TS 
~-Z sS 
PZ PIR =—~ E 2 
Nestling sparrow hawks. One-half natural size. 
alternated, the oldest bird being a male, the next a female, 
followed by another male, and so on; the last or youngest one 
of all five being a male. This last had a plumage of pure white 
down, with the pinfeathers of the primaries and secondaries of 
the wings, as well as the rectrices of the tail, just beginning to 
open at their extremities. From this stage gradual development 
of the plumage is exhibited throughout the series, the entire 
plumage of the males and the females being very different and 
