206 THE BIRDS OF SHERWOOD FOREST. 



have ascertained, as far as my inquiries have extended, 

 that the possession of one gland is confined (with some 

 exceptions, which I will mention presently) to those 

 birds which are strictly land feeders ; while those pro- 

 vided with two seek their food on the water. 



It may, perhaps, be considered that this fact goes to 

 strengthen the common opinion ; but let us examine it 

 a little closer. First, it is necessary for the maintenance 

 of this theory that the gland or glands should contain a 

 supply of oil sufficient for the constant requirements of 

 the birds ; and this, in those whose time is spent upon 

 the water, must be very large, for a daily application at 

 least would be needful to keep the feathers as repellant 

 as is requisite, to enable them to obtain their food and 

 to preserve that warmth and dryness which is essential 

 to their existence. But let any person ascertain by 

 actual experiment the quantity of oil contained in one 

 or both glands, and it will be seen at once that it is 

 totally insufficient for the alleged purpose, even in those 

 water birds which have the glands very large, as the 

 divers and grebes. "Willughby, I think, says that these 

 species, and such as want tails, have the glands small ; 

 but my experience is quite the contrary, and I believe 

 that the tail has nothing at all to do with the 

 question. 



But there is another difficulty. Supposing the ordi- 

 nary theory to be true, then all birds, and especially the 

 aquatic species, would make constant application to the 

 glands during the process of preening their feathers, in 

 order to obtain thence the oil for dressing them. This 

 I can venture to affirm is not the case. I have watched 

 various birds, both wild and tame, during this operation, 



