346 NATURAL HISTORY. 
the figure, the spines being forced out to make sure the 
hold. Ifthe animal caught be of sufficient size to require 
it, the other arms are thrown around it also, and the vic- 
tim is conveyed to the stomach. It has been observed 
that soft-bodied animals, if held for a little while in the 
arms without being swallowed, always die, even when 
released alive; from which it is inferred that the spines 
convey a poisonous secretion into the bodies of the prey, 
as do the fang of a serpent and the sting of a bee. As 
the Hydra can not do this to Crustaceans or any hard- 
shelled animals, they do not die at once on being swal- 
lowed; and so thin is the texture of the Hydra, that the 
outlines of these animals can be seen as they move about 
inside. 
601. The Hydra has some power of locomotion. When 
it wishes to change its place, it does it with a movement 
like that of the Geometrical Caterpillars (§ 479). Bend- 
ing its body forward, and taking hold either by its mouth 
or its tentacles, it raises its sucker, and advances it. 
Then, fastening itself again by this, it carries forward 
again the upper part of its body and the tentacles, and 
thus slowly moves to the desired spot. It takes several 
hours to march two inches in this way, and seven or 
eight inches may be regarded as a good day’s journey. 
But sometimes the Hydra gets along faster by executing 
a series of somersets, fastening himself by his tentacles, 
and then throwing his body forward. It sometimes, also, 
manages to sail along by a curious contrivance. It raises 
its flat sucker above the surface of the water, and letting 
it become dry, it acts as a sort of float, the animal hang- 
ing down in the water. In this way it can sail over con- 
siderable distances, either carried along by the wind blow- 
ing on the float, or by the tentacles acting as paddles. 
Though there is little of positive sensation in this animal, 
and therefore but a low degree of enjoyment, it undoubt- 
edly considers this ingenious way of sailing as one of its 
best sports. 
