MARSH TORTOISES. 21 



watchful, and on the slightest alarm they drop 

 almost imperceptibly into the water, and sink to 

 the bottom, whence they soon emerge if all is 

 quiet. They are voracious : their living prey is 

 taken, by stealing slowly towards it, and seizing 

 it with a sudden snap. 



It is a curious fact that whenever this Tortoise 

 eats a fish, it rejects the air-bladder ; and the 

 peasants, who seek these animals for the market, 

 judge of the number that are to be found in any 

 pond, by the number of fish-bladders floating on 

 the surface. Professor Bell has mentioned to us 

 that he had a Tortoise of this species in his pos- 

 session, to which he once threw six small living 

 fishes ; the next morning there was one fish re- 

 maining, and five air-bladders on the surface, told 

 the fate of the rest. 



Several genera of fresh-water Tortoises are 

 distinguished by their not being able entirely to 

 retract the head between the shields ; but they 

 obtain a partial protection by bending the long 

 neck to one side. In general the head in this 

 group is depressed, and the eyes are seated some- 

 what on the upper surface, so as to look obliquely 

 upwards instead of sidewise. These Tortoises 

 are, by some Naturalists, considered to form a 

 distinct Family by the name of Hydraspidce. 



