COLORATION 113 



This inference is by no means a good one. In spite of 

 the well-lighted position, the spots may, in such species, 

 still be necessary, for they were probably developed before 

 the birds adopted this more open nesting site ; and this 

 being so, the birds having during these early days learned 

 to depend on these guide-marks, they are still needed to 

 serve as a cue, so to speak, to the right co-ordination of 

 movements to-day necessary for the sure transference of 

 food to its destination. The fact that in some species, 

 as in wagtails, and the chaffinch, for example, no spots 

 are present, does not seriously affect the question. 



We may obtain a clue as to the origin of such markings 

 through such species as the white-throat {Sylvia cinered), 

 black-cap (5. atricapilla), garden warbler (5. hortensis) 

 and Orphean warbler {S. orphed), in which the tongue is 

 marked by an indistinct, and more or less perfect triangle 

 of a dusky hue. Surely these linear markings represent 

 an earlier phase of this colour-pattern. The spots arose, 

 in other words, by the concentration of the pigment to 

 form spots instead of bars ; while in certain species even 

 these have disappeared. In support of this suggested 

 course of evolution it may be mentioned that in certain 

 other species of warblers, e.g. reed-warblers {Acrocephalus 

 streperus) and the sedge-warbler {A. phragmitis) the 

 tongue is marked by a pair of small black dots placed 

 near its base. 



Herein we have a parallel to those cases where, by a dis- 

 integration of longitudinal stripes, a livery of spots and 

 mottlings has been evolved. These finally disappearing 

 leave the down whole-coloured. 



