THE PROBLEM OF THE ORIGIN OF SPECIES. 



29 



Similar vestiges are present in the mourning-dove, and here their identification 

 as marks formerly filled out with black pigment is freed from every shadow of doubt 

 by chequers in all stages of obliteration. (The conditions presented by Zenaidura 

 and Melopelia are fully discussed and illustrated in Chapter V. — Ed.) 



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

 widely from the turtle-dove 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 (see text-fig. 6, Vol. II) . The gray plumage and the white streak along 



Text-figure 8.— Adult white-winged pigeon, Melopelia leucoptera. x .77. The feathers at the lower outer edge of 

 the wing are white. No chequers in the adult, but structural imprints of these in a few feathers of the wing. 



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 (Cohmiba fasciata) of the Pacific coast, which is also a 

 species of turtle-dove derivation, 11 as shown in the neck-markings (see text-fig. 5, 

 Vol. II) and in the voice and behavior. 



These illustrations, which could be extended into the hundreds, may be con- 

 cluded with two cases, representing wide extremes, yet governed by the same law 

 of progressive orthogenetic variation. 



11 Minute blotches of black were found in the longer scapulars of a few individuals. These are probably atavistic 

 reminiscences of lost spots. 



