CGELENTERATA 



FIG. 18. Hydra: longitudinal section of ani- FIG. 20. Campanularian hydroid: 



mal showing m t mouth; /, tentacle; d, portion of colony, showing nutritive 



digestive cavity; b, bud; s, spermary ; zooids, _/; reproductive zooid, r ; 



o, ovary ; ec, ectoderm ; en, endoderm. young zooid, y ; and medusa, m 



Magnified. Magnified. 



FIG. 19. Hydroid (Sertularia) growing on a shell. 



FIG. 21. A Medusa, seen in 

 profile and from below, 

 showing central manu- 

 brium, radiating and mar- 

 ginal canals and tentacles. 



