BODIES OF BIRDS. 



251 



rior cellular membrane, especially in the neck and 

 axilla, which marks an analogy with the air-cells 

 under the skin of the bat. Winged insects, too, 

 have their bodies extended by air-cells communi- 

 cating with their respiratory apparatus. These 

 facts sufficiently evince the object of Nature in 

 this extension of the air-cells ; that it is not for the 



purpose of breathing, but for enlarging the volume 

 of the body without increasing the weight. 



