VAEIABLE KESEMELANCE IN VERTEBRATA, ETC. 105 



that other changes of colour do occur, as will be seen 

 in the following passage from his most interesting 

 paper. 1 



' Let any one who doubts the possibility of mark- 

 ings such as those on the Greenland Falcon becoming 

 gradually changed without an intermediate moult, 

 study the changes exhibited by the common Sparrow 

 Hawk in its progress towards maturity. The general 

 characteristic of the species of Accipiter is to have a 



striped plumage when young and a barred dress when 

 old. But it is not- generally known that this is 

 effected by a gradual change in the markings of the 

 feather, and not by an actual moult. On the first 

 appearance of the feathers from the downy covering 

 of the nestling, the markings on the chest are longi- 

 tudinal drops (fig. 18) of a pale rufous-brown colour. 

 The gradual dissolution and breaking up into three 

 bars is shown in fig. 19. Hence, when the bars are 

 perfectly developed a shade of darker brown over- 



(of Ptarmigan) gradually change colour in spring, only those being 

 moulted which have been injured in winter.' British Birds, vol. ii. 

 p. 427, n. 



1 Proc. Zool. Spc. 1873, pp. 414 et sec[. 



