HTDROZOA. 



109 



power of alternately raising and depressing its 

 hydrophyllia, so as to render them agents of pro- 

 pulsion. 



Fig. 22. 



Morphology of Physophobid^: — a, AthoryUa rosacea; b, 

 Physophora Pkilippii; o, pneumatophore ; v, nectocalyx; v\ rudi- 

 mentary nectooalyx ; <p, hydrocysts ; tt, polypite ; t, tentacles ; 

 3, hydrophyllia. (About the natural size.) 



