Biological Studies on Corymorpha. 407 



was not determined. There would seem to be more than an 

 accidental association in these widely separated organisms of 

 similar phenomena with similar structures. 



Another experiment demonstrated that a long exposure in an 

 inverted position to the influence of gravity has no effect on the 

 response of the individual when returned to normal conditions. 

 Two hydroids were suspended vertically upside down in glass 

 tubes, to prevent them from righting themselves. At the end of a 

 week they were freed, and oriented themselves normally. 



There are two elements in the stem to which the foregoing 

 results might be referable: the muscles, and the axial endoderm. 

 To solve the problem which thus presented itself the following 

 typical experiments were performed. 



A hydroid was decapitated and three wounds made at moderate 

 intervals half through the stem on one side. The stem bent 

 toward the opposite side, showing the greater potency of the un- 

 harmed muscles. When, however, it was laid upon the bottom 

 of the aquarium, wounded side uppermost, it assumed an erect 

 position in about an hour. It moved toward the muscularly 

 weaker side as rapidly as it would have done it had the stem been 

 intact. In whatever relation to the bottom the wounds were 

 placed, the stem regained a vertical position in about the same 

 time — in all cases very gradually. Another individual was cut in 

 a similar manner, though in this case there were eight or nine cuts 

 alternately on one side and the other. These cuts interrupted 

 the continuity of all the muscles except for very short distances on 

 the stem, which lay quite limp on the floor of the aquarium imme- 

 diately after the operation. Within two hours, however, it had 

 stiffened into an erect posture. The wounds in these cases did 

 not close for many hours after the stem had become erect. 



Only the continuity of the longitudinal muscles was broken by 

 the wounds, whose edges were drawn apart by the contracting 

 muscles. The axial cells not only maintained a continuous 

 column, but bulged out into the gaping wounds in the wall, under 

 considerable internal pressure. Since a stem mutilated on one 

 side may right itself when it is much contracted, and in this con- 

 dition the muscles as a whole on the wounded side are weaker than 



