HYDRA. 77 



gether without food. Stretching out its tentacles 

 in search of prey, and, finding none, it will gra- 

 dually accommodate itself to its abstemious con- 

 dition by diminishing its capacity, and so live on 

 till better times come round again. I have kept 



FIG. 13. 

 A. Hydra valgaris. B. Stinging organs magnified. 



Hydras in this semi-starved state for a long time 

 in perfectly clear water. They have nevertheless 

 multiplied, though getting, as they say, "small 

 by degrees and beautifully less" on water diet 

 only. 



There are two well-marked species of Hydra : 

 the one green, H. viridis, and the other white or 



