238 ALTERNATE GENERATIONS. 
between their different phases of existence was 
not understood, so that the same animal in differ- 
ent stages of growth has frequently been described 
as two or more distinct animals. This has led to 
a confusion in our nomenclature much to be 
rcgretted ; for, however inappropriate it may be, 
a name once accepted and passed into general 
use is not easily changed. 
That early stage of growth, common to all 
Radiates, in which they resemble the Polyps, has 
been called the Hydra state, in consequence of 
their resemblance to the fresh-water Hydra to be 
found in quantities on the under side of Duck- 
Weed and Lily-pads. For any one that cares to 
examine these animals, it may be well to mention 
that they are easily found and thrive well in 
confinement. Dip a pitcher into any pool of 
fresh water where Duck-Weed or Lilies are 
erowing in the summer, and you are sure to 
bring up hundreds of these fresh-water Hydra, 
swarming in myriads in all our ponds. In a glass 
bowl their motions are easily watched; and a 
great deal may be learned of their habits and mode 
of life, with little trouble. Such an animal 
soon completes its growth: for the stage which 1 
have spoken of as transient for the higher Radi- 
ates is permanent for these; and when the little 
sphere moving about by means of its vibratile 
cilia nas elongated a little, attached itself by the 
