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. Ever^- new habit should distinguish a bird ; for, 

 allowing for the tendencies of heredity, and the probability 



