CLASS HYDKOZOA. 



ii 



FIG. 15. 



the figure, or, better still, to the live animal, we notice 

 that it resembles the simple sponge in having an elon- 

 gated body, at the apex of which is 

 an opening. The radiate plan is 

 here shown in the disposition of the 

 long arms, or tentacles (ten'ta klz), 

 which surround the mouth-opening. 

 Other sponge-like characters are the 

 possession of a central cavity and 

 often the presence of small buds 

 attached to the side of the parent. 

 A further study, however, will re- 

 veal many things in the Hydra quite 

 different from the Sponge. 



There are no canals piercing the 

 sides of the animal, hence the food, 

 must enter in another way. If we 

 watch a Hydra which has become 

 attached to the side of a glass jar, 

 containing green slime and stagnant ng drafus'-ea hanging from an 



aquatic plant. B, Lower por- 



water from some pool, we notice tion of body, o, position of 



nl P -] TP mouth. A, One of the arms. 



that the small forms of animal life y , A " bud " partly expanded. 

 swimming around often become in- 

 active on approaching the Hydra, 

 being stung by the lasso-cells, and 

 are seized in the animal's tentacles 

 and thrust into the terminal opening, or mouth. The 

 food, much larger than that capable of being captured 

 by the flagellate cells of the sponge, passing through the 

 mouth, simply enters the bag-like body cavity, where it 

 is acted upon by the digestive fluids ; the hard, innutri- 

 tions portions being finally ' expelled through the same 

 opening by which they entered. Leading from the body 



showing disposition of two 

 cell layers around the central 

 cavity. (Enlarged about five 

 times.) 



