for food, almost to zero. The water snake, coiled up un- 

 der a stone at the bottom of a pond is not in a condition to 

 demand large supplies of oxygen. Still he requires some, 

 and a brief glance at his breathing apparatus will show us 

 where he gets it. Like most other serpents, he has only 

 one lung, the other being present merely as a rudiment. 

 This lung extends a good deal more than half tlu length of 

 'ais body, and the lower part is expanded into a membra- 

 nous sac, or bag, capable of containing a considerable 

 quantity of air. This bag stands Mr. Tropidonatus sipedon 

 in good stead in more ways than one. When he dives he 

 swallows his meal in a single mouthful, which is so ungen- 

 teelly large that it presses against his windpipe and stops 

 his breathing, so that for the time being he must get his 

 oxygen from his internal reservoir. Then when he makes 

 a voyage under water he can carry with him a cargo of 

 good fresh air. 



I have not compared the lungs of the water and land 

 snakes, but I imagine that very little difference would be 

 detected. Professor Agassiz made a very interesting series 

 of experiments with a view to determining the relative 

 lung capacities of land and water turtles. He proceeded 

 'by pumping ad the air from the living turtle, then pump- 

 ing them full of water, then pumping out and measuring 

 the water. He found that the capacity of the lungs of the 

 land turtle averages twice as much in proportion to the 

 weight of the body as that of the water inhabiting species, 

 although the sea turtles carry a sufficient supply of air in 

 their lungs to enable them to remain under water a half 

 ■hour or more. 



It will be found that water animals, as a rule, have their 

 •breathing organs much smaller than land animals. This 

 ■ apparent paradox is explained by the fact that a large 

 amount of oxygen may be absorbed by the skin from the 

 air diffused through the water. G. Brown Goode 



Smithsonian Institution, January 3, 1874. | 





