268 SCIENCE PROGRESS 



by the fact that its breeding range is mainly restricted to the 

 area extending from New York and Michigan northwards to 

 Labrador and Hudson Bay. 



The third, and perhaps most remarkable, example relates 

 to the so-called Inca or scaly dove (Scardafella inca), one of 

 two species whose united range extends from the south of 

 Texas and Arizona in the north to Brazil in the opposite 

 direction. The typical bird extends from Texas to Nicaragua, 

 where, and in Honduras, it is replaced by the race known as 

 S. i. dialeucus. Farther south, on the island of Marguerita and 

 the Venezuelan coast, we find a second species, S. ridgzvayi, 

 which, in its turn, is replaced in Brazil by the race S. r. 

 brasiliensis. Within their respective localities these four forms 

 appear to be perfectly constant in the matter of general 

 colouring and markings ; S. inca, to put it shortly, having 

 almost uniformly light under-parts, while in S. ridgzvayi the 

 same region is marked by a number of transverse dark flecks, 

 which also extend on to the wing-feathers. 5. i. dialeucus and 

 S. r. brasiliensis, it should be added, are intermediate in 

 these respects between the Texan and Venezuelan birds. As 

 regards minor details of marking, such as the relative amounts 

 of black and white on the wing-feathers, there is, however, 

 great individual variation even among birds from identical 

 localities. 



When specimens of the typical Inca dove were confined in 

 a super-humid atmosphere, a radical change in the pigmentation 

 was observed to take place with each succeeding annual moult ; 

 while a change apparently similar in extent and direction re- 

 sulted from an artificially induced monthly replacement of the 

 plumage. At the first annual moult the bird was brought very 

 close to the Scardafella inca dialeucus type ; at the second moult 

 the colour-pattern approximated either to the Brazilian or 

 the Venezuelan phase of S. ridgzvayi; while after subsequent 

 changes the plumage became more profusely and heavily marked 

 than in any of the normal wild representatives of the genus. 

 Intrinsically the change appears at first to be a segregation 

 and intensification of the black pigment, resulting in an exten- 

 sion and clearing-up of the white or whitish areas. Next ensues 

 a brief period of equilibrium, succeeded by such an increase 

 of the black pigment that the latter begins to encroach upon 

 the light areas on the quill and tail feathers, till eventually 



