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. 



B 



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- 



