HEREDITY 89 



which inherit their cries never imitate the notes of 

 other birds. It is probable that the birds which now 

 inherit cries have always done so, and that the notes 

 have been partly developed by the agency of selection, 

 acting on slight and accidental modulations ; for, 

 despite the force of inheritance, variations are of 

 frequent occurrence. 



It might be well here to notice that there are some 

 species of song-birds in which both cries and songs 

 are perpetuated, not by heredity, but solely by imita- 

 tion, though whether the mimicry is voluntary or 

 involuntary would be difficult to prove. 



It will be observed that the young of certain 

 species, such as the fowl, pheasant, partridge, turkey, 

 swan, duck, cuckoo, etc., though inheriting the notes 

 of their parents, do not at first utter all of them, but 

 gradually acquire them in course of progress towards 

 maturity. This feature may be consequent upon 

 physical development ; but the young of the golden 

 plover, lapwing, tinamu, and oven-bird possess, as 

 we have seen, the full notes of their parents. This 

 divergence of habit cannot be attributed to any 

 difference in the relative size of the species, for the 

 tinamu is nearly as large as a fowl; but it indicates 

 that the cries most fully uttered by the young have 

 been inherited during the longest period. 



