52 LIFE AND HER CHILDREN. 
sible to find, either hanging from under the leaves 
of the common duckweed, or clinging to pieces of 
floating stick, or rooted to stones at the bottom 
of the pond, a little greenish being (Fig. 19), about 
a quarter of an inch long, looking like a tube with a 
circlet of feelers at the end, which are waving in the 
water. This creature is the common pond hydra, and 
it is in fact nothing more than a tube or sac, with a 
sucker at one, end to hold on with, and a number of 
jelly-arms or tentacles at the other, which serve to 
catch its food, and to tuck it into the sac, where it 
is digested. The walls of the sac are firm and mus- 
cular, and the creature can stretch itself out, or draw 
back at will, can move along slowly by means of its 
sucker, and even float upon the water; but the most 
remarkable thing about it, and the one we wish to 
study- now, is the power which it has of overcoming 
animals stronger and more active than itself. 
Groping about with" its flexible arms, which are 
covered with fine jelly- hairs by which it seems to 
feel, it touches perhaps a water -flea, a water -worm, 
or even a tiny newly -born fish, passing by in the 
water. Instantly it twists its arms round whatever 
it finds, and though its prey may struggle vigorously 
while the hydra remains almost still, yet little by 
little the struggles cease, and the victim is drawn 
into the fatal sac. 
Now, why is this ? It is because those fine 
tender feelers of the hydra are full of lassos, which 
it can use with as good effect as any skilled hunter. 
Although to the naked eye each tentacle looks but 
little more than a fine hair, yet, when examined 
under a strong microscope, it is seen to be crowded 
