94 KINSHIP OF BIRDS, AS SHOWN BY EGGS. 
correlated with a few, comes in the egg—modified perhaps 
as much by the bird’s habits as by anything else—the most 
variable of the variables—swayed this way and that within 
an extremely limited range of variations, progressions and 
reversions in both the bird and itself, and tied down often 
by a heredity so purely physiological as to be beyond the 
reach of all the external influences of such environments as 
often make the bird a new creature. If Mr. Wallace’s views 
be correct—and within limits they seem to be—the egg may 
be influenced by habits of the parent that have been brought 
about independent of the needs of the egg. By either his 
view or that of Darwin, the color of the bird, either male or 
female, which has been superinduced by sexual or protec- 
tive selection—an influence clearly outside of the egg’s de- 
velopment or adaptation—may so shape the nest as to ren- 
der the color of the egg and its surroundings entirely in- 
congruous. The influence of migration will be noticed 
further on. This much has been said in order to show with 
what encumbrances the egg enters the field. Habit is its 
greatest foe—a giant towering away above structure or 
morphological variation. Habit is more flexible than hered- 
ity or than the fixing of variations through adaptation to 
environment. Much as we may sneer at the old systems, 
more of our modern taxonomy is based on habit than we 
might be willing to admit. We still group for instance the 
Owls in the Raptores. Perhaps we cannot do better; but 
quite likely all that holds them there is their specialization 
as prey-takers—an adaptation wrought by environment upon 
an altogether different class of material from that in the rest 
of the group. Their eggs, by the way, strongly hint this. 
So since we now feel that so much of adaptation is the re- 
sult of persistent habit, and that adaptation is so large a 
factor in structure, we might well correlate habit along with 
structure, at least as a differentiating characteristic—if not 
an element. Every new habit should distinguish a bird ; for, 
allowing for the tendencies of heredity, and the probability 
