. The dynamics of living matter. Biochemistry; Reproduction; Regeneration (Biology). 124 DYNAMICS OF LIVING MATTER directed upwards. If such a colony is put horizontally into an aqua- rium which receives its light from above in the direction of the arrow cd, Fig. 24, it will be observed that very soon the heads of the worms are turned upward so that the axis of symmetry is in the direction of the rays of light. Very soon the tubes begin to grow in front through the deposition of new lime salts (which are secreted by glands). But the direction of this growth is now at right angles to the longit
. The dynamics of living matter. Biochemistry; Reproduction; Regeneration (Biology). 124 DYNAMICS OF LIVING MATTER directed upwards. If such a colony is put horizontally into an aqua- rium which receives its light from above in the direction of the arrow cd, Fig. 24, it will be observed that very soon the heads of the worms are turned upward so that the axis of symmetry is in the direction of the rays of light. Very soon the tubes begin to grow in front through the deposition of new lime salts (which are secreted by glands). But the direction of this growth is now at right angles to the longitudinal axis of the old tubes. This again shows that the primary effect of the light in the heliotropic reactions is the bending of the tip, or head, of the animal through protoplasmic or muscular contraction. The bend- ing of the tube or growth are secondary phenomena which follow the former. I believe that the phenomena of heliotropism of sessile animals and plants are essentially alike. The presence of nerves in animals is no reason for denying this identity, especially since some botanists, Hildebrandt, claim that tissues which functionally resemble nerves also exist in FlG. 24. — Positive heliotropism of Serpula uncinata. The light had originally struck the animal in the direction of the arrow at, and their tubes were parallel with the direction of the rays. When the light fell in the direction cd the tubes began to grow at right angles to their former direction. Partly diagrammatic. 2. HELIOTROPISM OF FREE-MOVING ANIMALS \ We have seen that the essential feature of the heliotropic reaction consists in the fact that the light automatically puts the plant or the animal (Eudendrium, Spirographis} into such a position that the axis of symmetry of the body, or organ, falls into the direction of the rays of light. In the case of positively heliotropic organs, the tip, or head, is directed toward the source of light, while it is the reverse in the case of negative
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