THE ORIGIN AND RELATIONSHIP OF THE ROCK-PIGEONS. 59 



the Chinese turtle-dove (Sp. chinensis) the spots have been completely obliterated 

 (pi. 23, fig. A). The neck-spots have been carried to higher and higher stages of 

 differentiation in these four species, and in the order mentioned, 12 so that there can 

 be no doubt as to the direction of modification. 



The large wood-pigeon (Columba palumbus) of Europe has departed still more 

 widely (text-fig. 6, Vol. II) and evidently from the same type, having lost all its black 

 spots, except a few in the neck patches, which have retreated so far from the tips 

 of the feathers as to be concealed. The gray plumage and the white streak along 

 the edge of the wing mark a plane in the evolution of this bird very nearly identical 

 with that of the white-winged pigeon. A little higher plane has been reached by 

 our band-tailed pigeon (Columba fasciata) of the Pacific coast, which is also a species 

 of turtle-dove derivation, as shown in the neck-marking and in the voice and 

 behavior (text-fig. 5, Vol. II). 



The ring-doves forming the large genus Streptopelia, embracing thirteen 13 species, 

 are a branch arising directly from turtle-dove ancestors. They have all lost their 

 dark spots everywhere except in the black collar, and the only remaining visible 

 trace of the spots elsewhere is the narrow light edge shown at the tip of each feather 

 in the juvenal plumage (pi. 8, Vol. II). 



The little red ring-dove (Streptopelia Jmmilis) stands nearest to the turtle- 

 doves, both in color (pi. 21, Vol. II) and behavior. In this species the red is but 

 an extension and intensification of the light edge of the turtle-dove feather. 

 Lifting the scapulars and inner secondaries, we still find obsolete remnants of the 

 dark centers, which have been so reduced as to be wholly concealed by the over- 

 lying feathers. The shaft of the feather still remains dark, while in the common 

 cage ring-dove even this reminiscence of the dark spot has been bleached. 



In the ring-dove species the reduction process has not only washed out the 

 spots, but also advanced from the darker brown-red to gray, isabelline, and blond, 

 and finally to pure white. Albinism is the finishing stage of the process we have 

 been following. In the common domestic doves it advances through paler and 

 paler shades of gray, the bars growing always narrower. The white rump in the 

 rock-pigeon has followed the pale-gray rump, and this the darker gray. The white- 

 edged wing seen in many wild species has succeeded the gray-edged wing, and this 

 sequence is still often shown in passing from juvenal to adult plumage. 



The spotted type originated in a marginal reduction of pigment, beginning at 

 the apex of the feather and extending along both sides. Further reduction advanced 

 in the same direction, and so evenly on both sides as to leave the longitudinal axis 

 of the spot generally coinciding with the shaft of the feather. The main advance 

 of the process as a whole was antero-posterior in direction, while in the individual 

 feather it was primarily and predominantly in a postero-anterior direction — i.e., from 

 the apex towards the base. The opposition in direction is apparent rather than real; 

 the free end of the feather is first in development, and hence the direction of reduction 

 is here the same as that of development, as it is in the case of the body as a whole. 



The chequered pattern of the rock-pigeon originated from the spotted type, by 

 division of the single central spot into two lateral spots. The general course of 



12 These neck-murks are fully illustrated and their behavior in hybridization is fully described in Chapter XVII, 

 Vol. II.— Ed. 



u Seventeen species were later recognized; see Chapter XV, Vol. II. — Ed. 



