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. 



FIG. 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 its 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- 



