758 Birds, 



concealed by the water. And granting that water-fowl are able to 

 " expel at pleasure the air within the various cavities of the body," 

 and that the body so exhausted of air is compressible, still I contend 

 that the lungs must be free to play; and that, therefore, the body, as 

 to its principal cavity, can never be exhausted, and consequently not 

 much, if at all, compressed. And hence I infer that the whole body 

 can never be reduced to nearly the same specific gravity with water : 

 and if not, it will be impossible for the bird to maintain itself in a 

 state of submergence.* 



So much for the inferential part of the arguments. Let us now 

 turn to the practical ornithologists' best friend and guide, observation, 

 or rather, to its results. Of course a moorhen, when diving, has 

 freed itself of its " buoyancy and resistance to the water" (Zool. 668), 

 by expelling the air from " within the various cavities of the body ;" 

 and consequently, according to W. H. S.'s theory, must be specifi- 

 cally nearly as heavy as water. Well, I will shoot a moorhen in the 

 act of diving, and will add to its specific gravity by depositing within 

 its body some twenty or thirty grains of No. 5 shot. Of course then 

 it will sink ; and unless my retriever is a rather uncommon one I lose 

 the bird. But no such thing ; the moorhen comes to the surface 

 immediately, and floats almost as buoyantly as ever : and yet whence 

 and how can the air have been procured, which has been applied to 

 the replenishing of the air-vessels, and the restoration of the bird's 

 buoyancy ? I do not ground my argument upon the fact of the moor- 

 hen's coming to the surface when shot in its concealment among 

 weeds : for since it is an incontrovertible fact, that they do make use 

 of the weeds to hold themselves down by, it is thence clear, that even 

 if they are capable of expelling their internal air, as W. H. S. sup- 

 poses, they are not in the habit of doing so when concealing them- 

 selves in the vicinity of weeds. 



Again, I have had some experience in shooting birds of the diver and 

 duck kinds on the sea ; and yet I never saw any one of them attempt 

 to place itself in a state of submergence in the open sea. As to 

 diving, that is another question ; as also it is with respect to partial 



* I do not wish to except from this reasoning the divers, grebes, and cormorants, all 

 of which swim with their bodies very deep in the water ; still less the pochard or 

 dunbird, and allied species, which, from the shape of their bodies, appear to " draw 

 more water" than most others of the duck tribe. — See Selby's Orn. 111. vol. ii. passim. 

 What system of air-cavities have the divers ? 



