WINGS AND FEET 
used for propulsion under water. The penguins, 
although entirely distinct from the auks, fly 
through the water with their extended flipper- 
like wings, and, from the testimony of those 
who have watched them in tanks, it is learned 
that the feet are not used. Thus Lea? says of 
these curious birds: ‘‘ Their flight may be 
watched and studied in the large glass tanks 
at the Zoo. .. With short, rapid strokes of 
its paddle wings it darts through the water 
leaving a trail of glistening bubbles behind, 
and shoots forward with the speed ofa fish, turn- 
ing more rapidly than almost any bird of the 
air by the strokes of the wing alone, the legs 
floating apparently inert in a line with the 
gleaming body, or giving an occasional upward 
kick to force it to greater depths.” 
One is apt to assume that “the trail of 
glistening bubbles ” which comes from a diving 
bird are the expired air bubbles, but I am 
inclined to think that most if not all of this 
air is expelled from the feathers in order to 
make diving more easy or even possible. Some 
diving birds have the ability to sink gradually 
out of sight in the water with apparently little 
1John Lea, The Romance of Bird Life, 1909, pp. 202-203. 
191 
