120 



TWO-LAYERED ANIMALS— PHYLUM COELENTERATA 



like those of an octopus, will wrap themselves around the unfortunate 

 water flea and the now insensible victim will be carried to the mouth by 

 the tentacles for ingestion. 



Nematocysts 



Mesoglea 



Older 

 bud 



Gland cell 

 Ectoderm 



■Flagellated celt 

 Ovary 



Egg-cell 

 •Basal disc 



Animal Biology, Wolcott, McGraw-Hill Book Co., Inc. 



Fig. 9.2. Diagram of a longitudinal section of hydra bearing a testis, ovary, and 



two buds. 



With respect to digestion, hydra is a transitional form. Ingested 

 food passes into the gastrovascular cavity, where it is exposed to extra- 

 cellular enzymes which flow out of the cells lining this cavity. These 

 enzymes, however, accomplish only a partial digestion. When the 

 food is broken down into small bits, these small particles will be en- 

 gulfed by the cells which line the cavity in much the same way as 



