938 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 
regretted ; 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 
growing 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 I 
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 has elongated a little, attached itself by the 
