206 THE ZOOLOGIST. 



item, for a flat-bottomed vessel floats higher than one of the 

 same weight with a deep and narrow body. Of course, the 

 Duck can alter the outward shape of its waterproof " feather 

 film " at will. 



I offer the above remarks as an attempt to solve a problem 

 that has for long puzzled ornithologists. I have explained how 

 a Grebe may use its clumsy toes, and how a Moorhen actually 

 does use them ; indicated the use of the cilia and other feather 

 elements in keeping the plumages of all birds waterproof, and 

 showed that this power is not dependent on the grease. Finally, 

 I point out how the actual submergence of a swimming or 

 floating bird is due to the height of its specific gravity, and how 

 this is readily adjusted within the necessary limits by the volun- 

 tary act of the bird. 



