B 



FIG. 51. Hydra. 



A, Two living specimens of H. viridis attached to a bit of weed. 

 The larger specimen is fully expanded, and shows the elongated body 

 ending clistally in the hypostome (hyp), surrounded by tentacles (t], and 

 three buds (bd l , bd-, bd*} in different stages of development : a small 

 water-flea (a) has been captured by one tentacle. The smaller specimen 

 (to the right and above) is in a state of complete retraction, the tentacles 

 (t) appearing like papillae. 



B, H.fusca, showing the mouth (mth) at the end of the hypostome 

 (hyp], the circlet of tentacles (t}, two spermaries (spy], and an ovary 

 (pvy}. 



C, a Hydra creeping on a flat surface by looping movements. 



D, a specimen crawling on its tentacles. 

 (C and D after W. Marshall.) 



