14 



HYDRA 



It is uncertain, however, how far these species are really 

 distinct from one another, and the following description will 

 apply to any one of them. 



Fig. 4.— Hydra. A diagrammatic longitudinal section of a specimen with 

 ripe reproductive organs, and with a fully formed bud ; x 12. (a. m. m.) 



A, mouth. B, hypostome. C, body-cavity. D, ectoderm. E, mesoderm. 

 p, endoderm. Cr, cavity of one of the tentacles. H, testis. I, ripe ovum in 

 the ovary. K, fully-formed hud, with mouth and tentacles. It, foot by which 

 the Hydra is attached to a piece of weed. 



I. EXAMINATION OF A LIVING SPECIMEN. 



Cut off a small piece of weed with a Hydra attached to 

 it ; place it on a slide in a drop of water, and put on a cover- 



