CHAPTER IV. 



THE HYDRA AND JELLY-FISH. 



The common Hydra (Fig. 21) may be found in f resli-watei 

 ponds attached by its base to the under side of the leaves 

 of aquatic plants. It is not fixed 

 permanently, but can move freely 

 about. It is very small, just large 

 enough to be seen without a magni- 

 fying-glass; it is usually pale green, 

 but is sometimes brown. The mouth, 

 which is surrounded with from five 

 to eight tentacles or feelers, opens 

 into the central cavity or stomach. 

 The Hydra, attached to some leaf, 

 reaches its tentacles out in all direc- 

 tions; a minute insect or young snail 

 or Infusorian passing by will, if 

 touched by these feelers, be instantly 

 paralyzed, and then the feelers close 

 over the helpless victim and it is 

 drawn into the stomach and digested, 

 la. 21.— Bj/dra, with two This powcr of paralyzing and thus 



young (o, o) budding from -"^ . . ,T' . 



it; t, tentacles surrounding easily capturmg active living crca- 



the mouth, 

 fled.) 



(Much magni- 



tures is due to the presence in the 

 skin of the tentacles and body of what are called lasso-cells 

 or nettling organs (Fig. 23, c, d, «), which are minute cells 

 containing a long barbed thread coiled up within the cell. 

 When the Hydra touches an animal swimming near it, 

 thousands of these little barbed cords are darted into the 



