92 REPTILIAN WATER TRESPASSERS. 



of wood about two incites wide, and extending along 

 the whole of the foot. On either side was a piece of 

 very thin but strong board, making the whole appa- 

 ratus about eleven or twelve inches in width. The 

 side pieces were attached by hinges, so that when the 

 feet were drawn forward, they collapsed, and offered no 

 resistance to the water, while they opened out again in 

 making the stroke. Flat pieces of board were also 

 attached to the hands ; and by means of this apparatus 

 a wonderful rate of speed could be attained. 



Still, ingenious as was the invention, it is infinitely 

 surpassed by the structure of the Frog's hind feet, 

 which have also the advantage of being useful on land, 

 whereas the swimming apparatus just mentioned 

 would render its wearer incapable of advancing ten 

 steps on land. 



Another point in the structure of the Frog is the 

 mode of its breathing. It has neither diaphragm nor 

 ribs, and cannot, therefore, respire by means of either 

 the one or the other. It is, however, compensated for 

 their absence by the great development of the throat- 

 bone called os hyoides, and the muscles connected 

 with it. By their action the large throat is converted 

 into a sort of bellows, by means of which air is forced 

 into and drawn out of the lungs. Anyone can see 

 this movement by watching a Frog or a Toad. 



In consequence of this structure, added to the 

 large size of the cellular lungs, the fore part of the 

 body is rendered very light, and is the better able to 

 sustain the animal in the water. Like many semi- 

 aquatic creatures, the Frog can float on the surface of 

 the water, or lie on the bed of the pond or stream, the 



