144 COLLEGE ZOOLOGY 



temperature, to mechanical stimuli, to chemical stimuli, and to 

 gravity. Reproduction is both asexual, by budding and fission, 

 and sexual, by means of eggs and spermatozoa. 



Economic Importance. - - Ccelenterates as a whole are of very 

 little economic importance. The coral built up by coral polyps 

 form reefs and islands and thick strata of the earth's crust. 

 Some corals are used as ornaments and for the manufacture of 

 jewelry (Fig. 89, C). Ccelenterates are probably very seldom 

 used as food by man but are eagerly devoured by fishes. 



