132 BRITISH BIRDS. 



the open air does not necessarily militate against this 

 interpretation : for they may be regarded as survivals of 

 an earlier phase when such marks were useful. Like 

 many other characters now useless, they may have sur- 

 vived because their suppression has not been necessary 

 for the welfare of the species. 



The wide, highly-coloured membranous flanges that 

 occur at the gape of all nestlings of the helpless type may 

 also be regarded as adaptations to facilitate the work of 

 feeding. If they also are indeed guide-marks, it would be 

 interesting to discover whether they are larger in those birds 

 whose mouths are not conspicuously coloured inside. But 

 the want of information on this subject is deplorable, and 

 it is to be hoped that those who have suitable opportunities 

 will hasten to fill this gap in our knowledge. Notes 

 concerning this coloration should always be made having 

 regard to the nature of the nesting site and the relative 

 amoimt of light which reaches the interior of the nest 

 and its occupants. 



Whenever possible photographs should be taken. But 

 this will be found a task which will tax even the most 

 skilled photographer. Probably none but those who have 

 attempted, or may attempt, this feat will appreciate 

 the skill and labour which Miss E. L. Turner has expended 

 on the photographs which illustrate this article, and I 

 should like to take this opj)ortunity of expressing my 

 thanks to her ; these pictures having been taken after an 

 immense amount of trouble, in response to my apjjeal to 

 Miss Turner for help. So far as I know they are, of their 

 kind, unique. 



{To he continued.^) 



