268 FACULTIES OP BIRDS. 



CHAPTER XXI. 



FLIGHT OF BIRDS. 



THE flying of a bird in the air is performed on 

 similar principles to that of a fish swimming in the 

 water, with this difference, that the bird is more 

 heavy, in comparison with the air, than the fish in 

 comparison with the water. At first view, it might 

 be thought impossible for so huge an animal as the 

 Ostend whale (Balanoptera loops ?), weighing four 

 hundred and eighty thousand pounds, to swim in 

 the sea, considering that its body, so far as the 

 bones and muscles were concerned, must have been 

 considerably heavier than water. Yet, by a singu- 

 lar contrivance, it is at once buoyed up in the sea, 

 and rendered so much lighter than water, that it 

 floats on the surface when dead. This consists in 

 an enormous layer of an oily substance called blub- 

 ber, immediately under the skin. We are well jus- 

 tified in using the epithet " enormous," from the 

 fact that in the Ostend whale the blubber measured 

 four thousand gallons, and weighed a twelfth of the 

 whole body. With a large proportion, therefore, of 

 a light body like this to buoy it up, so far from find- 

 ing it difficult to swim, it would require a great ef- 

 fort in order to dive deep into the water. 



In fishes (for the whale, being a warm-blooded 

 animal, and breathing the air, is not considered a 

 fish), the buoyancy indispensable for swimming is 

 effected by a very different contrivance. A blad- 

 der, varying in form in different species, is filled 

 with air (azote in fresh water, and carbonic acid gas 

 in marine, fishes), over which the animal appears to 

 possess a voluntary power, either to empty it by 



