40 University of California Publications. [zoology. 



Two individuals were suspended by a string so that the stems 

 pointed directly downward. Within seven hours both had as- 

 sumed horizontal positions. At the end of thirty hours one was 

 bent sharply upon itself so that the distal four-fifths of the stem 

 was vertical, the knot by which the animal was tied interfering 

 with the assumption of a vertical position by the entire stem; 

 the other polyp was extended upward at an angle of 45? On the 

 following day both were as nearly vertical as the knot would 

 allow; and so they remained until released several days later. 



To determine whether the sensitiveness to the stimulus of 

 gravity was local or general, three polyps were transversely 

 sectioned, the first just below the hydranth, the second half way 

 down the stem, the third near the base. They were placed in 

 the dark in an airtight jar, which was set at different angles as 

 in the first experiment. Like results followed. Each piece 

 responded, the shortest taking the longest time to become erect, 

 the longest one the shortest time, but all finally arranging them- 

 selves in line with the pull of gravity. 



To determine whether the muscles of the stem or the vacuolated 

 endoderm cells (skeletal cells) respond to the stimulus of gravity, 

 the following experiments were made. An individual was decap- 

 itated, and cuts were made on one side at three levels, half 

 through the column, thus destroying the continuity of the muscle 

 layer on that side in three places. The muscles contracted 

 between the wounds, causing them to gape; the gaps were 

 soon filled by skeletal cells. The column bent toward the side 

 opposite the wounds showing the greater potency of the uncut 

 muscle layer. When, however, it was laid upon the bottom of 

 the aquarium, wounded side uppermost, it assumed an erect 

 posture in about an hour — moving toward the muscularly weaker 

 side. 



Another individual was cut in a similar manner, though there 

 were eight or ten cuts, alternately on one side and the other. 

 These cuts interrupted the continuity of the muscle layer on the 

 entire circumference except for very short distances. The column 

 lay quite limp on the floor of the aquarium immediately after the 

 operation. Within two hours, however, it had stiffened into an 

 erect posture, though the wounds had not closed. 



