YOUNG BIRDS AND RECORDS OF THE PAST 149 



diving habits, as a device for preventing the entrance of 

 water into the nostrils during prolonged submergence. 



The similar loss of external nostrils in the gannet and 

 pelican we might have explained on the same grounds, 

 since these birds dive for their food from a height, and 

 might be supposed to require protection from the entrance 

 of water into the windpipe no less. But the tropic-bird 

 (PhiSthon), a near relation of the gannet, and the king- 

 fisher also dive in like fashion, and have open nostrils. 

 Similarly, the guillemot and razor-bill, the grebes and 

 divers and many species of ducks, have to procure their 

 food by prolonged submergence, like the cormorant and 

 the penguin, and they have open nostrils ! 



Here, then, is a case which seems to defy interpretation, 

 and one, moreover, which has no parallel among verte- 

 brates. The process of closing revealed by a study of 

 nestling birds reveals some interesting facts, but so far 

 it throws light only on one aspect of the phenomena. It 

 is surely not a little surprising that these facts should 

 have remained so long unnoticed, for there are no other 

 instances known among land vertebrates where the 

 respiratory air is drawn in solely by the mouth. A careful 

 examination of the nostrils of diving birds which remain 

 open may show that some mechanism hitherto unsus- 

 pected may exist whereby the nostrils can be closed, as is 

 the case with the seals, for example, during the time of 

 submergence. 



During all my life nestling birds, and their later 

 " flapper " stages, have exercised a peculiar fascination 

 for me : at first for reasons which I could not explain ; 

 later for the light they shed on the various evolution 

 problems which form so piquant a sauce to the otherwise 

 insipid meat which must form so much of the mental 



