. Studies in general physiology. Physiology; Phototropism; Geotropism; Reproduction; Irritability; Regeneration (Biology). 154 Studies in General Physiology in the screen, or to move off the screen entirely. If, as soon as the animal has assumed the position shown .in Fig. 26, the wire screen is turned over so that the foot of the animal is directed upward, the foot is not withdrawn, but begins to bend vertically downward from the tip. The bend- ing then passes from one ele- ment of the body to the next, from the foot to the head. As soon as the tip of the foot again touches the screen, it pus
. Studies in general physiology. Physiology; Phototropism; Geotropism; Reproduction; Irritability; Regeneration (Biology). 154 Studies in General Physiology in the screen, or to move off the screen entirely. If, as soon as the animal has assumed the position shown .in Fig. 26, the wire screen is turned over so that the foot of the animal is directed upward, the foot is not withdrawn, but begins to bend vertically downward from the tip. The bend- ing then passes from one ele- ment of the body to the next, from the foot to the head. As soon as the tip of the foot again touches the screen, it pushes itself through it as far as pos- sible. If the wire net is again turned over, the whole process is repeated anew. In this way the animal can be compelled, by the help of gravity alone, to weave itself through the meshes of the screen several times "of its own ; Fig. 33 shows a Cerianthus which has thrice passed through the meshes of the screen in this way. The drawing is taken from life. 4. Such a bending downward, which has been accurately studied in negatively geotropic roots, has never been demon- strated, so far as I know, in animals. I will therefore cite another experiment which better illustrates the course of this reaction. If a Cerianthus be put into a test-tube filled with sea-water, and the test-tube be placed so that the head of the animal is down and the foot up, while the long axis of the animal is vertical, the tip of the foot begins after some minutes to bend vertically downward. In Fig. 34 is shown the course of such an experiment. Several minutes before 12 o'clock the animal was placed in a test-tube in the posi- tion described. At 12 the foot of the animal had begun to bend downward (Fig. 34, a); in the next thirteen minutes the bending gradually advanced toward the head (Fig. 84, b). Digitized by Microsoft®. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - color
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