34 ANIMAL FORMS 
process bearing on its end an opening which becomes the 
mouth (Fig. 18, A). Around the margin of the bell nu- 
merous tentacles develop, and at the same time the gelati- 
nous substance situated between the outer and inner layers 
of the bell expands to a relatively enormous degree, giving 
it an increasing globular form and glassy appearance. 
Fic. 18.—A jelly-fish (Gonionemus), slightly enlarged. The stalked mouth is shown 
in dotted outline. B, C, enlarged portions of a hydroid colony bearing the 
mouth and tentacles; j, a capsule within which the jelly-fish develop ; D, dia- 
gram of jelly-fish, illustrating 1ts method of locomotion. 
Finally, vigorous movements rupture the connection with 
the parent, and this newly developed outgrowth, usually 
small, becomes an independent organism popularly termed 
a jelly-fish. While the external form of the jelly-fish appears 
to be widely different from the hydranths, a more careful 
study shows the difference to be superficial. Some zoolo- 
gists believe that jelly-fishes are simply buds which have 
become fitted to separate and swim away from the colony 
in order to distribute the young, as described hereafter. 
When the stalked colonies are very abundant the jelly- 
