19^ 
LECTURE XIL 
ence in many other genera of zoophytes more oi* 
less allied to it. 
The genus Hydi'a or Polype, eomprehending 
the real or fresh-water polypes, was so named by 
Linnseus because in reality it affords phenomena 
similar to those recorded of the fabulous Hydra of 
antiquity, which, when one head was cut off, pro- 
duced others in its place. The character of the 
Hydra or Polype is a long, tubular body, possessing 
a great power of contraction and extension j affix- 
ing itself by the tail ; and furnished at its upper 
or open end with a certain number of long arms 
or tentacula, differing in number in the different 
species. The principal species are the brown, the 
yellowish-grey, and the green Polypes, or the Hy- 
dra fusca, grisea, and viridis of Linnceus. These 
curious animals may be found in small streams 
and in stagnant waters, adhering to the stems of 
aquatic plants, or to the under surfaces of the 
leaves, and other objects. They prey on small 
worms, Monocuii, and many other animals which 
iiappen to occur in the same waters. If a Polype 
be cut in two, the superior part will produce a 
new tail, and the inferior part will produce a new 
head and arms ^ and this, in warm weather, in the 
