254 A HISTORY OF BIRDS 



direction of the stripes was a matter of prime importance. The 

 widespread occurrence of longitudinal stripes probably depends 

 on a deeper stimulus. 



The definite and orderly sequence of colour, which many 

 animals exhibit in the course of development, seems to show 

 that in many cases the markings of the immature stages are 

 really reproductions of an ancestral adult livery. This is well 

 seen in cases where the male and female have a distinct livery. 

 Here the females and young are often precisely similar in dress, 

 and bear a remarkably close resemblance to the adult stages of 

 both sexes of more primitive but closely allied species. Among 

 birds there are many illustrations of this. A large number of 

 animals, however, afford no clue as to whether the colour of 

 the immature individual is ancestral or newly acquired ; whether 

 it is an ancestral adult ox an ancestral y«:'fcv///t' coloration. The 

 larval Alpine Newt, for example, is conspicuously longitudinally 

 striped. Even while still within the Qg^ these markings can 

 be seen. There is a median dorsal black stripe, which bifur- 

 cates on the head, and a lateral stripe, also black. Later, black 

 pigment cells wander into the transparent ground colour, and 

 eventually the black upper and red under-surface of the adult is 

 acquired. The stripes of caterpillars are not easily accounted 

 for. Are these independently acquired markings, or inherited 

 ancestral larval markings? They certainly can have nothing 

 to do with the adult coloration. 



With the birds the problem becomes still more complex, 

 inasmuch as, in the precocious types at least, we may have three 

 separate plumages: {a) the nestling; (/;) of the fully-fledged 

 "immature" stage, which may be the same as that of the 

 female ; and {c) the adult stage, i.e., the plumage worn by the 

 male only, or by both sexes. 



With regard to the " immature " stage it is worthy of com- 

 ment that, as Professor Newton has pointed out, " Throughout 

 the Class Aves it is observable that the young, when first fledged, 

 generally assume a spotted plumage of a peculiar character — 

 nearly each of the body feathers having a light-coloured spot 

 at its tip — and this is particularly to be marked in many groups 

 of the oscines. . . ." 



There seems to be strong presumptive evidence to show 

 that the primitive coloration of young birds took the form of 



