ANIMAL BIOLOGY 



How many mature hydranths are seen in the hydroid 

 shown in Fig. 40? Why are the defensive hydranths 



on the outside of the 

 colony ? Which hy- 

 dranths have no tenta- 

 cles ? Why not ? 



Jellyfish. Alterna- 

 tion of Generations. - 

 Medusa. With some 

 species of hydroids, a 

 very curious thing hap- 

 pens. The hydranth 

 tJiat is to produce tJie 

 eggs falls off and be- 

 comes independent of 



the colony. More sur- 

 prising ^ ^ appear _ 



FIG. 43- - A JELLYFISH. 



ance changes entirely and instead of being hydra-like, it 



becomes the large and complex creature called jellyfish 



(Fig. 43). But 



the egg of tJie 



jellyfish pro- 



duces a small 



hydra- like ani- 



mal 'which gives 



rise by budding 



to a hydroid) 



and the cycle is 



complete. 



The bud (or 

 reproductive 

 hydranth) of 

 the hydroid FIG. 44 . A JELLYFISH (medusa). 





