YOUNG BIRDS IN THE NURSERY 73 



display a marvellous solicitude for the welfare of their 

 young, and instances of this have already been given in 

 these pages, there are one or two acts of peculiar interest 

 and significance which must find a place here, even though 

 it is true they concern the attitude of the parents to their 

 young, rather than the behaviour of the young them- 

 selves, which forms the theme of these pages. 



The first of these acts concerns the sanitation of the 

 nest, and in this the nestlings themselves play a very 

 important, though unconscious part, at least in the case 

 of nestlings of the helpless type — for example, among the 

 Passerine birds, such as, for instance, thrushes, finches, 

 warblers, and so on. In how far it applies to others, 

 equally helpless, which belong to that other great, non- 

 Passerine, but nearly related congeries of types, represented 

 by, say, the woodpeckers, swifts, and so on, we do not know, 

 and this because ornithologists, so far, have been more 

 keen on taking eggs and killing adults than on observing 

 their habits. The exceptions to this rule are happily 

 numerous, and to them we owe the little that we know on 

 this subject already. 



The sanitary measures in question concern the removal 

 of excrement from the nest. And the unconscious part 

 played by the nestlings, just referred to, consists in the 

 fact that in their case the excrement is surrounded by a 

 white jeUy-Uke mass enclosed within a delicate, film-like 

 envelope or pellicle. No one has yet analysed the com- 

 position of this protective covering, nor has any one yet 

 explained how or whence it is formed. Possibly it is 

 secreted by the walls of the cloaca, but we cannot resist 

 a suspicion that it may be formed within a curious pouch 

 known as the Bursa Fabricii, and forming a capacious 

 chamber above the cloaca, and opening into it. So far 



