ox TIIF. Srr.MRROF-XCE OF WATEn-BIRPS. 



In speaking of the Purple Gallinule, (Gallinula viartinica,) ho says "It runs 

 with gi*eat speedy and dives with equal address ; often moving off under water 

 with nothing but the bill above." Again, he says of the Common Moorhen, 

 (O. Chloropus) "At all other times when raised, they suffer their legs to 

 dangle, proceed slowly to a short distance, and drop among the reeds, or if 

 over water, they dive and hide, leaving nothing but the bill projecting above 

 the surface." One more and I have done. The Clapper Eail, (R. Crepitans,) 



^'It dives well, remains a 

 considerable time under wa- 

 ter, and in this manner 

 dexterously eludes its pur- 

 suers j when hard pressed 

 it often sinks just below 

 the surface, keeping the bill 

 above in order to breathe ; 

 and in this position, if not 

 detected, remains for a con- 

 siderable time; if perceived 

 and approached, it instantly 

 dives, and uses its wings to 

 accelerate its progress, but 

 rises as soon as it comes to 

 a place of safety." These extracts all shew a wonderful power of control over 

 their specific gravity in birds, which are, except the first, only moderately, 

 aquatic in their habits and conformation, and which one would hardly expect 

 to exhibit the highest development of diving powers. 



Before entering upon the mode in which the bird accomplishes this state 

 of submergence, it may be well to remark, that birds in addition to the air 

 contained in the lungs, are also furnished with large cavities called air cells, 

 in every part of the body, where they do not interfere with the organization of 

 the part. These air cells communicate with the lungs, but do not appear 

 to be capable of being emptied of the contained air by the will of the bird. 

 The bones and the barrels of the feathers are also full of air, so that the 

 bird is naturally a good deal lighter than water, and cannot sink without 

 some effort on its own part. 



I will now proceed to consider the main subject of inquiry, namely, how the 

 bird probably may be supposed to alter its buoyancy to such an extent as 

 to enable, it to maintain the whole of its body just beneath the surface of 

 the water. It is manifest to any one who is at all conversant with the laws 

 of hydrostatics, that in deep water this can only be accomplished in one of 

 the following ways, by either of which the body of the bird might be supposed 

 to be rendered of, as nearly as possible, the same specific gravity as the water 

 in which it swims: — 



1st. — The bird might expel so much air from its body, as to remove its, 



