204 LAND AND FRESH-WATER MOLLUSKS. 
It is a very active creature, and ascends at 
will to tlie surface in a direct line, or returns to 
the bottom, or holds itself suspended in the 
water, with facility; its habits maybe well ob¬ 
served in the aquarium. The above-mentioned 
movements of this snail are, according to Mr. J. 
Jones, effected in the following manner: “ The 
edges of the foot are brought closely together, 
converting that member into a tube, from which 
the column of water therein enclosed is expelled 
with considerable force, either upwards or down¬ 
wards, as the animal may be disposed to ascend 
or descend, being, in fact, a modification of the 
mode of locomotion adopted by the cuttle-fish, 
which effects its rapid movements by ejecting 
water through a funnel.” The Pisidiums , the 
glass-bubble shell, and some of the pond- 
snails, as previously stated, exhibit the same 
powers; and it is the accepted explanation, that 
the snail does so by means of glutinous threads. 
Mr. W. Nelson charges the present species with 
cannibalism; he writes, * * * * “ on looking 
again, three or four days after, I found some more 
shells empty, but this time caught five or six of 
the real delinquents busily feeding on the dead 
body of one of their comrades, and* one of the 
empty shells had a rather large hole in the whorl 
next to the body-whorl.” 
