HYDRA AND OBELIA. POLYPS AND MEDUSA. 175 



--ect. 



-end. 



perith. 



Fig. 109. — Part of a colony of Obelia, magnified. 



bl., Blastostyle ; ect., ectoderm ; end., endoderm ; gtk., gonotheca ; hyth., 

 hydrotheca med., medusa bud ; p.b., polyp bud ; ferith., peritheca. 



