. The dynamics of living matter. Biochemistry; Reproduction; Regeneration (Biology). HELIOTROPISM 137 where, on account of the refraction of light, the intensity is a relative minimum.* The fact can be demonstrated still differently: if one part of the aquarium is covered with an opaque body, these organisms gradually gather under the covered part, where they come to rest. If the cover is suddenly removed, they w~ w begin to become restless and creep about. In heliotropism we deal with an automatic orientation of the animal by light, which compels all the animals to move in the same direction.
. The dynamics of living matter. Biochemistry; Reproduction; Regeneration (Biology). HELIOTROPISM 137 where, on account of the refraction of light, the intensity is a relative minimum.* The fact can be demonstrated still differently: if one part of the aquarium is covered with an opaque body, these organisms gradually gather under the covered part, where they come to rest. If the cover is suddenly removed, they w~ w begin to become restless and creep about. In heliotropism we deal with an automatic orientation of the animal by light, which compels all the animals to move in the same direction. In animals like earthworms or Planarians this orienting effect of light is very slight, and the animals may or do move in every direction. Of course, it is possible that sensitiveness to sudden changes in the intensity of light exists also in a heliotropic animal. Serpula uncinata is positively heliotropic, and yet contracts rapidly when the inten- sity of the light is suddenly decreased. In Planarians the sensitive- ness to changes in intensity prevails, while, according to G. H. Parker, they show a slight degree of negative heliotropism. * Loeb, Pfliiger's Archiv, Vol. 53, p. 81, Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Loeb, Jacques, 1859-1924. New York, Columbia University Press
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