4o6 Harry Beal Torrey. 



Several uninjured hydroids and three (Fig. i) which had been 

 cut respectively two-thirds, one-third, and one-eighth the length 

 of the stem from the proximal end, all weighted with sand as 

 usual, were placed in a dark closet in a jar full of water. As soon 

 as they became erect, the jar was tilted at an angle of forty-five 

 degrees, the stems of the hydroids remaining parallel with its 

 sides. In an hour all the stems had become erect. The distal 

 pieces cut from the three mutilated stems were still lying on the 

 bottom, unable to rise for lack of hold-fasts. The jar was brought 

 back to the vertical, and in another hour the stems had swung 

 through forty-five degrees to the vertical, in the opposite direction. 

 The time required for such changes varies considerably, but in the 

 same experiment the shorter the piece the longer the time — ten to 

 twenty minutes longer in the case described. The movement was 

 constantly toward, never away from, the vertical position finally 

 assumed, and did not suggest in the slightest the method of trial 

 and error (Jennings, '04). 



The time required for an inverted hydroid to right itself is much 

 longer. Two hydroids, hung vertically by a string tied to their 

 proximal ends, were horizontal within seven hours, inclined up- 

 ward at an angle of forty-five degrees in thirty hours, and vertical 

 in their normal position in forty-eight hours. In another experi- 

 ment the hydranths and hold-fasts were removed from two 

 hydroids which were hung on a thread piercing them near their 

 proximal ends. They righted themselves in twenty-four hours. 

 When hung from strings around their necks, the stems remained 

 as they were, vertical, whether they possessed hydranths or not. 

 A stem lacking both hydranth and hold-fast was pierced through 

 the middle by a glass needle which was suspended horizontally. 

 In an hour the stem was vertical, distal end up, and remained thus 

 for several days. 



Fig. I shows fairly well the important fact that it is unmistak- 

 able in the animals themselves, that the stem in turning toward 

 the vertical does not bend locally but generally. Corymorpha 

 resembles the stems of plant seedlings in this respect, as well as 

 in the preliminary bending of the stem beyond the vertical. 

 Whether the bending travels progressively from oral to aboral end 



