20 



ZOOLOGY. 



Class I. — Hydrozoa. 



Characters of Hydrozoans. — The common Hydra (Fig. 18) 

 may be found in fresh-water ponds attached by its base to the 



Pig. 16.— Hydra fusca, with two young (a c) budding from it; b, 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 



