66 A NATURALIST IN BORNEO 



absent from the ventral surface of embryos and nest- 

 lings, and these parts are covered with feathers in the 

 adult. It is clear therefore that the ventral feather- 

 sheaths of the adult are not produced into trichoptiles, 

 and this is probably due to mechanical reasons. The 

 embryo lies in the egg in a curled-up position, the 

 head being bent over to cover the belly in part, and 

 consequently there is no room for a dense mane of 

 trichoptiles to develop, as on the back. Moreover, the 

 young nestling squirms about on its belly and chest, 

 and a trichoptilar covering of these parts would quickly 

 be worn off ; as it is, the dorsal mane soon becomes 

 sadly rumpled and abraded. It is reasonable to suppose 

 that ventral trichoptiles are not developed, because if so 

 they would be worn away on, or soon after, their first 

 appearance. As the nestling grows older the horny 

 feather-sheaths push through the skin ; those on the 

 dorsal surface are rufous with black bands, while the 

 ventral ones are cream-coloured ; the trichoptiles are 

 now very short, and before long they entirely disappear. 

 When finally the feather-sheaths are shed the young 

 Bubut appears in a livery of yellowish red, banded 

 with black, and it is a year before the adult colours 

 are assumed. The significance and purpose of the 

 trichoptiles is quite unknown to me ; they do not 

 serve to render the nestlings inconspicuous, quite the 

 reverse ; the nestlings, being buried in a deep nest 

 hidden in dense grass, are presumably independent of 

 adventitious aids to concealment ; and the fact that 

 the trichoptiles are far better developed in the embryo 

 than in the nestling seems to dispose of the suggestion 

 that their purpose is to aid the mother-bird in deter- 

 mining the exact position of her young, shrouded in 

 the obscurity of the nest. 



