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ZOOLOGY. 
Class I. — Hydhozoa. 
Characters of Hydrozoans. — The common Hydra (Fig. 18) 
may be found in fresh-water ponds attached by its base to the 
t 
Fig. 16.— Hydra fusca, with two young (a c) budding from it; 6, the base; «, the 
digestive cavity; t, tentacles. Magnified. 
under side of the leaves of aquatic plants. It :s not fixed 
permanently, but can move freely about. It is very small, 
just large enough to be seen without a magnifying glass; 
it is usually pale green, but is sometimes brown. The 
