ORGANS OF BREATHING. 65 



cells, the legs and even toes partaking of the same 

 singularity, so that it appears much larger than it 

 really is, and when pressed by the finger, the skin 

 sinks in, but resists pressure like a foot-ball, or other 

 elastic body. The air, in this case, is supposed to 

 assist in producing a powerful screaming voice, the 

 bird being a wader, and not calculated for lengthened 

 flights. 



Generally speaking, the bones of birds, excepting 

 when young, are without marrow, the gradual absorp- 

 tion of which, till the bones become a hollow tube, 

 is most easily perceptible in young tame Geese, when 

 killed at different periods of the autumn and winter. 

 From week to week the air-cells increase in size, till, 

 as the season advances, the air-bones become trans- 

 parent. Towards the close of the summer and 

 beginning of autumn, although in external appear- 

 ance the young Goose resembles the parent, no trace 

 of air-cells can be discovered in its bones, the in- 

 terior being still filled up with marrow, which does 

 not entirely disappear till about the end of the fifth 

 or sixth month. 



In the Eagle, Hawk, Stork, Lark, and other birds 

 in the habit of soaring, the air-cells are very large, 

 particularly those in connexion with the wing. On 

 the other hand, Ostriches, and those birds which 

 either never, or seldom fly, those of the wing are 

 comparatively small ; but as a compensation, it has 

 been remarked, that as great strength as well as 

 lightness are desirable to enable them to run swiftly, 

 their bones are almost all of them remarkably hol- 

 low. Such are some of the advantages derived from 

 this abundant supply of air. 



VOL. I. F 



