THE WONDER OF LIFE 549 



precise movements, such as placing food in the nestling's 

 mouth. It was Alfred Russel Wallace who first expounded 

 the theory of recognition colours, bringing forward in- 

 stances, especially from among deer, antelopes, birds, and 

 insects, of striking patches of colour which may be plausibly 

 interpreted as facilitating rapid recognition. One of the 

 best instances is also the most familiar the rabbit's 

 upturned white tail. When they are feeding in the twilight 

 and are suddenly alarmed, safety may depend on the 

 rapidity with which they reach the burrows. Hesitation 

 may be quite fatal, and it does not seem far-fetched to 

 suppose that * the white, upturned tails of those in front 

 serve as guides and signals to those more remote from 

 home, to the young and the feeble '. The white stripe 

 above the springbok's tail, which is nearly concealed when 

 the animal is at rest, but very prominent when it starts to 

 run, is probably another good instance. 



In Mr. W. P. Py craft's fine History of Birds, which is a 

 rich treasure-house for students of adaptations, attention 

 is called to the bright colours sometimes seen around or 

 in the mouth of nestlings ; and the interpretation is offered 

 that they serve as a guide to the parents when feeding the 

 young. The inside of the mouth is diversely coloured, e.g. 

 bright yellow, as in the thrush, and purplish-red, as in the 

 chaffinch, while in the Bearded Titmouse it is of ' a bright 

 cornelian red, surrounded by a band of yellow, and relieved 

 by a double row of white, glistening, tooth-like conical 

 processes '. It seems that the most elaborate oral decor- 

 ations, as in the Gouldian Weaver-finch (Poephila gouldii), 

 are found in young birds which are hatched in places where 

 there is but little light. Chun has noted that in this bird 

 the brilliant bodies at the angles of the mouth of the nestling 



