24 



HTDROZOA. 



Fig.^, 



Morphology of Hydea : — a, Hydra vulgaris, with a young 

 polypite sprouting from its side, attached to a piece of stick ; b, 

 portion of a tentacle ; c, one of its larger thread-cells ; d, H. vi- 

 ridis, on a fragment of an aquatic plant, with elevations contain- 

 ing spermatozoa arising near the bases of the tentacles, between 

 which and the attached extremity one side of the body-wall is 

 seen to be much distended by an ovum ; e, this ovum, ruptured ; 

 f, spermatozoa escaping from their receptacle, burst under pres- 

 sure, (a is about twice the uatiiral size ; the others are much 

 magnified.) 



