28 



the water for a distance three or four times the height of 

 the polyp. Figure 13 shows a hydra with the tentacles 

 fully extended, and their tips touching the ";round. This 

 is the habitual attitude. The drooping of the tentacles is 

 evidently caused by their extraordinary length, and is al- 

 most as unusual an occ rrence among the hydromedusae. At 

 the points where the tips of the tentacles come in contact 

 with the bottom they spread out somewhat, forming a sole- 

 like surface v;hich is closely applied to whatever object 

 the polyp is settled upon (Fig. 13 P.T). This smearing out 

 of the tentacle-tips is like what occurs in live specimens 

 of Hydra held between slide and cover-glass for examina- 

 tion. It is not known that the cells at the tip of the 

 tentacle of Gonionema undergo tr^insformation to form gland- 

 colls and an adhesive organ, but such a change seems at 

 least possible. At any rate, the fact is that the habit ot 

 the polyp is much like that of the medusa; both remain when 

 at rest with the mouth expanded, the manubrium stretching 

 upv/ards, the tentacles widely extended and adhering to the 

 bottom. When an animal swims against one of the tentacles, 

 the reactions are much the same in polyp and adult. The 

 feeding habits of Gonionema have been described at length 

 by Yerkes (Sensory Reactions in Gonionemus " - 1902). His 



