RADIATES. 345 
repore were spoken of as blossoms of stony plants. It 
is now about a century since their animal character was 
really admitted by naturalists; and it is only quite re- 
cently that their structure and habits have been thor- 
oughly investigated. 
599. The Polypes, or Zoophytes, have the most simple 
construction of all animals, but they differ from each oth- 
er in the degree of their simplicity. The most simple of 
all are the Hydras—little Polypes which you can find in 
stagnant waters. In Fig.270 you have a representation 
of one of these. The smaller 
figure shows it of the natural 
size. It is a simple sac or 
purse-like animal, with a mouth, 
and tentacula arranged around 
the mouth. With these tenta- 
cles or arms the animal catches 
its prey, and puts it mto its 
stomach through the mouth, a. 
§ In its general shape, and in the 
working of the arms, it is much 
like the Cuttle-fish (§ 550). Its 
tentacles are, however, armed 
in a very different manner. 
They have neither suckers, like 
Hig. 20 — Hydra: those of the Cuttle-fish, nor cil- 
ia, like those of many animals, but minute bristles, and 
sharp, firm spines, curiously arranged. These spines are 
concealed in wart-like processes when they are not in 
use, but they can at any time be thrust out, just as the 
claws of a carnivorous animal are protruded from their 
concealment when their services are needed. 
600. When the Hydra is searching for prey, it allows 
its tentacles to float about in the water, its body being 
fastened by a sucker to some solid substance. If a Crus- 
tacean or an aquatic worm happens to hit one of them, 
the arm is immediately thrown around it, as you see in 
2 
