Page:Natural History, Reptiles.djvu/29

Rh 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 possession, to which he once threw six small living fishes; the next morning there was one fish remaining, 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 somewhat 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 Hydraspidæ.