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 

 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 Hydra3, 

 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 



