860 Mr. C. Ingram on the [Tbis^ 



on the spinal tract are not marginally situated when the 

 contour-feathers appear. As these latter grow the down- 

 tufts are carried on their extremities and are forced relatively 

 lower down the back (c/. figs. 3 A and 3B). 



As the time approaches for the Passerine fledgeling to 

 leave its nest, the neossoptiles are shed by abrasion. Those 

 subject to the greatest amount of friction — i. e., on the 

 ventral and femoral tracts — disappear first, while those on 

 the head, owing presumably to the fact that they cannot be 

 reached when the bird is preening its plumage, are generally 

 retained the longest*. 



It is my belief that the downy integument found in the 

 majority ol' Passerine nestlings is not, as some would suggest, 

 a functionless ancestral inheritance, but is usually of real 

 service to the species possessing it. Its jjriucipai purpose 

 seems to be undoul)tedly that of concealment, although the 

 retention of heat in the body is probabl}^ an important 

 secondary use. 



In some cases the obliterative effect of this downy covering 

 is really remarkable, and it is certainly curious that this fact 

 has not been commented on before. Take, for instance, the 

 helpless young of Passerine species nesting in deep recesses, 

 such as concavities in a bank, under overarching tufts of 

 grass, or, again, in dense and low herbage. These are almost 

 always clothed in a loose down of a dusky neutral grey or 

 blackish colour. When in ie[)ose a nestful of such birds, 

 huddled together, counterfeit with extraordinary fidelity 

 a patch of deep shadow. In fact, I do not think it con- 

 ceivable tliat there could be any more perfect device for 

 reproducing the effect of depth witiiout form, than this 

 downy mass with its appearance of filmy darkness. In 

 other words, the shadows of the natural recess in whicii the 

 nest is ensconced remains virtually undisturbed, and the 

 chance of detection is reduced to a minimum. Good 

 examples may be fouiul among the Pipits, Eunlings, 



* In a domestic fowl tliat liad oue of its legs iujiired as a chick, so 

 that it was incapable of scratching its head, I noticed that the neossop- 

 tiles on the crown were retained for many months. 



