134 ANIMAL ACTIVITIES. 
that of an inverted hydra, with a greatly overgrown foot- 
forming the covering of the umbrella. These jelly-fish 
are often called medusz, because in some similar forms 
the long tentacles around the edges of the umbrella 
covering are supposed to resemble the snaky locks of 
the mythical monster. The tentacles surrounding the 
umbrella of the Campanularian medusze are not large, 
but they have at their bases minute spots connected 
with nerve-masses. These are thought to be eyes or 
Fic. 113.—Medusz of Campanularium Hydroid (Zucope diaphana). a, 
whole colony, one half natural size; 4, single zooid magnified; 
A, young medusa magnified; 2, adult medusa magnified. After 
Agassiz. 
ears. These jelly-fishes swim through the water with 
a slow flapping of the umbrella edges. 
After a time eggs are produced which float out into 
the water and produce, not jelly-fish, but the branching, 
fixed Campanularians. Thus the young resemble the 
grand-parents instead of the parents. The children of 
these young, however, resemble the jelly-fish. Such 
a phenomenon is not uncommon in the animal world 
and is called alternation of generations. 
Scyphozoa. Besides the jelly-fish just described 
there are other free-swimming medusz whose origin is 
