130 STRUCTURE OF HYDRA, 
require separate notice. The group of Hydrozoa, or Hydroid 
= so named from the little Hydra, or fresh-water 
polype, which may be regarded 
as its type, will be first described 
on account of its near con- 
nexion with the preceding. The 
Hydra (fig. 71) is a solitary 
polype, not at all uncommon 
in ponds or other collections of 
fresh water, where it is found 
attached to aquatic plants, or 
to floating sticks, straws, &c., 
by means of a kind of sucker 
at its lower extremity, stretching 
out its tentacles in search of its 
food, which consists of minute 
aquatic wormsand insects. These 
are securely laid hold of by one 
or more of the tentacles, and are 
Fig. 71.—Hypra, or Fresu-water drawn into the mouth, a, which 
ab ic leads to the stomach or general 
cavity of the body, in which they are digested, and from 
the walls of which the nutritious portions are absorbed, the 
portions of the food which are not eapable of being digested 
being cast out through the mouth. 
122. The Hydra multiplies in two ways; namely, by gem- 
mation or budding, and bya proper generative process. Little 
bud-like processes are developed from various parts of the 
walls of the stomach, which gradually assume the form of the 
parent, possessing a mouth surrounded by tentacles, and a 
digestive cavity which is at first in connexion with that 
of the parent; the communication is gradually cut, off, how- 
ever, by the closure of the canal of the footstalk of the young 
polype ; and ere long the footstalk itself separates, and the 
young polype henceforth leads an entirely independent life, 
Not unfrequently, however, the young polype itself puts forth - 
buds before its separation; and as many as nineteen young 
Hydre, in different stages of development, have been seen to 
be thus connected with one and the same stock, Another 
very curious endowment of the Hydra depends upon the same 
facility of developing the whole structure from any part of it ; 
