54 



HYDROZOA. CALYPTOBLASTEA 



— 10 



--- 9 



.-8 



Fig. 12. Part of a branch of Obelia. Enlarged. To the left a portion 

 is shown in section. (After Parker and Haswell.) 1, ectoderm ; 

 2, endoderm ; 3, mouth ; 4, coelenteron ; 5, ccenosarc ; 6, perisarc ; 

 7, hydrotheca ; 8, blastostyle, a mouthless polyp bearing medusa- 

 buds ; 9, medusa bud ; 10, gonangium or gonotheca. 



