26o COLOUR IN NATURE chap. 



paper on the subject, adopts the view that longi- 

 tudinal striping is the most primitive condition, that 

 this tends to develop into a spotted condition by 

 the suppression of portions of the stripe, and that 

 the fusion of spots gives rise to cross -striping. 

 Kerschener, on the other hand, regards cross-striping 

 as the primitive condition from which spots are 

 derived. In point of fact, the distinction is perhaps 

 less important than it seems, for Hacker's conception 

 of waves of pigmentation passing down the shaft 

 might equally be regarded as resulting in longi- 

 tudinal striping, or in a very primitive form of cross- 

 barring. Hacker's observations were made chiefly 

 upon nestlings of thrushes and chats (Turdidae and 

 Saxicolinse), and also upon certain of the Limicoline 

 birds. His researches lead him to regard the most 

 primitive form of colouring as that seen in some of 

 the downs of the Limicolse, such as Podiceps ruhri- 

 collis, where there is merely a little pignient collected 

 at the tip of an otherwise colourless down. This is 

 his primary pigmentation. Most downs, however, 

 show, on the other hand, in addition to this terminal 

 patch of pigment, a basal pigmented area due to the 

 process of secondary pigmentation. In this way is 

 produced the characteristic appearance of the feathers 

 of young thrushes, where there is a pigmented downy 

 area, and then a clear colourless area defined by a 

 terminal pigmented band. Besides occurring in the 

 young of the thrushes and their allies, this type of 

 coloration is found in the adults in the simplest 

 feathers, such as those of the cheeks, the chin, etc. 

 The primary pigment may form a dark spot at the 

 apex of the feather, giving the plumage a spotted 



