HYDRA. 



19 



I 



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

 distinct from one another, and the following description will 

 apply to any of them. 



Fia. 12. 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, enteron or digestive cavity, d, ectoderm. 

 E, mesogloea. Fi endoderm. G, cavity of one of the tentacles. H, testis. 

 I, ripe ovum in the ovary. K, fully formed bud, with mouth and tentacles. 

 L, 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 a cover-glass 



