Abstract
WE have measured in various parts of the spectrum the amounts of radiation necessary to elicit in the planarian Dendrocoelum lacteum, a characteristic response, namely, movement away from a source of light1. In each trial, one animal was dropped into a square ‘Perspex’ tank (50 cm. × 50 cm., 10 cm. deep) filled with lake water, in front of a calibrated source of spectral radiation placed outside the tank (opal electric bulb, ‘neutral’ wedges and colour filter2). D. lacteum, being milky-white in colour, could readily be detected with a red electric torch against the background of black paper placed under the tank. After 3 min. the torch was switched on and it was seen whether the animal had moved at least 10 cm. away from the light source in approximately the right direction. If so, this was taken as a positive response. The animal's movements were too slow for the observations to be appreciably affected by the light of the torch. In control experiments in which the colour filter was replaced by a piece of opaque cardboard, the number of animals giving a positive response was insignificant.
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PIRENNE, M., MARRIOTT, F. Light Sensitivity of the Aquatic Flatworm Dendrocoelum lacteum . Nature 175, 642 (1955). https://doi.org/10.1038/175642a0
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DOI: https://doi.org/10.1038/175642a0
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