271 
HYDR2E, OR FRESH- WATER POLYPES. 
extraordinary extensibility of these organs may be doubted. 
Some have supposed that the water which finds its way into 
the cavity of the hydra's body through the mouth, may flow 
in extremely narrow channels into the tentacles, and thus 
occasion their elongation. The tentacles of Hydra fusca 
(Polype a longs bras of Trembley), are the most wonderful of all 
for their extensibility ; growing gradually finer than the lightest 
gossamer, they become invisible except to the eye of the 
micro scopist. 
The hydrse are very voracious, and may be kept readily in 
confinement for some time. They feed on the small ento- 
mostraca, such as daphnia , cyclops , cypris , &c., and on minute 
larvge of gnats and naid worms. The stomach of these 
animals is a simple cavity, though some authors have re- 
corded the existence of a short narrow duct leading from the 
stomach to the centre of the disc which they say is per- 
forated, and that through this aperture excrementitious 
particles may be seen to pass. I have been quite unable 
to discover any signs of an intestinal canal in any of the 
species I have examined; further evidence is wanted before 
this statement can be accepted. The food is quickly assimi- 
lated by the hydra, and the indigestible portion expelled 
through the mouth as in the actinice. There is no doubt as 
to the existence of the thread-cells before alluded to, but 
some persons, and conspicuously Mr. Gr. H. Lewes, entirely 
deny that they have stinging properties. ee That the tentacula 
have the power of communicating some benumbing or noxious 
influence to the living animals which constitute the food 
of the hydra," says Professor Owen, “is evident from the 
effect produced, for example, upon an entomostracan which 
may have been touched but not seized by one of these 
organs. The little active crustacean is arrested in the midst 
of its rapid darting motion, and sinks apparently lifeless for 
some distance; then slowly recovers itself and resumes its 
ordinary movement. Siebold states, that when a nai’s, a 
daphnia, or the larva of a clieironomus have been wounded 
by the darts, they do not recover, but die. These and other 
active inhabitants of fresh water, whose powers should be 
equivalent to rend asunder the delicate gelatinous arms of 
these low- organized captors, seem paralyzed almost imme- 
diately after they have been seized, and so countenance the 
opinion of Corda, that the reaction of a poison enters the 
wound." Trembley nowhere states that animals once caught 
in the hydra's embrace always died, nor does he allude to any 
stinging or poisoning power of the hydra. 
Baker says, “ I have now and then seen a very strong 
worm seized by a small polype break off all the polype's 
