W. p. PYCRAFT : NESTLING BIRDS. 131 



of the Pied Wagtail are among those species with unspotted 

 mouths, but the colouring is very striking, being of a 



Fig. 2. — Nestlings of Bearded Tits, showing the Spots on the Tongue 

 and Palate. (From a Photograph by Miss E. L. Tueneb.) 



luminous gamboge yellow, outlined by the pale yellow of 

 the gape flanges. 



As above remarked, the conspicuous coloration of the 

 inside of the mouth appears to be most strongly developed 

 in those nestlings which are reared in dimly-lighted 

 places, and it may well be that this colour has been 

 developed to serve as a guide mark to the parents when 

 feeding their yomig. Without such an aid, indeed, 

 the food might as often be dropped outside the nestling's 

 mouth as within it. The fact that such guide- 

 marks are foiuid to-day in nestlings which are reared in 



