. The dynamics of living matter. Reproduction; Regeneration (Biology); Biochemistry; Reproduction; Biochemistry. 122 DYNAMICS OF LIVING MATTER We find heliotropic curvatures in animals where there can be no doubt that the curvature is due solely to a process of contraction, and not to a process of growth. Spirographis Spallanzani is a marine Anne- lid from lo cm. to 20 cm. long, which lives in a rather rigid yet flexible tube. The latter is formed by a secretion from glands at the surface of the animal. The tube is attached by the animal with its lower end to some solid body, while the other e
. The dynamics of living matter. Reproduction; Regeneration (Biology); Biochemistry; Reproduction; Biochemistry. 122 DYNAMICS OF LIVING MATTER We find heliotropic curvatures in animals where there can be no doubt that the curvature is due solely to a process of contraction, and not to a process of growth. Spirographis Spallanzani is a marine Anne- lid from lo cm. to 20 cm. long, which lives in a rather rigid yet flexible tube. The latter is formed by a secretion from glands at the surface of the animal. The tube is attached by the animal with its lower end to some solid body, while the other end projects into the water. The worm lives in the tube and only the gills, which are arranged in a spiral at the head end of the worm, project from the tube. The gills, how- ever, are quickly retracted, and the worm withdraws into the tube when touched or if a shadow is cast upon it. When such tubes with their inhabitants are put into an aquarium which receives light from one side only, it reqtiires, as a rule, a day or more until the foot end of the tube is again attached to the bottom of the aquarium. As soon as this occurs, the anterior end of the tube is raised by the worm until the axis of sym- metry of the gills falls into the direction of the rays of light which enter through the win- dow into the aquarium (Fig. 22).* When the animal has once reached this position it retains it as long as the position of the aquarium and the direction of the rays of hght remain unchanged. If, however, at any time the aquarium is turned 180° so that the light falls in from the opposite direction, the animal bends its tube during the next twenty-four or forty-eight hours in such a way that the axis of symmetry of its circle of gill? is again in the direction of the rays of light (see Fig. 23). When the hght strikes the aquarium from above, the animals assume an erect position, like the positively heliotropic stems of plants when they grow in the open. In these phenomena the mechanical pro
Size: 2356px × 1061px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, booksubjectreproduction, bookyea
