. The dynamics of living matter . Fig. 23. If such a secretion occurs on one side of the tube only, or more so than on the opposite side, the former must become shorter than the latter, and the result must be a curvature of the tube, that side becoming con- cave where the new secretion has occurred. On this assumption, which is based on many observations, the pro- cess of heliotropic curvature is in this case as follows: when the light strikes the circle of gills from one side only, in these elements certain chemical re- actions occur more quickly, or to a larger extent, than on the opposite s
. The dynamics of living matter . Fig. 23. If such a secretion occurs on one side of the tube only, or more so than on the opposite side, the former must become shorter than the latter, and the result must be a curvature of the tube, that side becoming con- cave where the new secretion has occurred. On this assumption, which is based on many observations, the pro- cess of heliotropic curvature is in this case as follows: when the light strikes the circle of gills from one side only, in these elements certain chemical re- actions occur more quickly, or to a larger extent, than on the opposite side. This results in correspond- ing alterations of the sensory nerve endings, the sensory nerves, and the corresponding motor nerves, and their muscles. The sense of these changes is such as to throw the muscles connected with the nerves of the gills on the light side into a more powerful tonic or static contraction than the muscles on the opposite side of the body. The consequence is a bending of the circle of tentacles, or the head, toward the source of light, which will continue until the axis of symmetry of the circle of tentacles falls into the direction of the rays of light. When this happens, symmetrical tentacles are struck at the same angle (or in other words with equal intensity) by the rays of light, and therefore the tone (state of contraction) of the antagonistic muscles is the same. The result is that the circle of tentacles becomes fixed in this position. The bending of the head produces an increased pressure and friction of the animal against that side of the tube which is directed toward the light, and this pressure and friction lead to an increased secretion and the formation of a new layer inside the tube. Observations on another marine worm which lives in a stony tube, Serpula uncinata (Fig. 24), add an interesting detail.* These worms occur in colonies of thousands whose tubes are in close contact. The tubes of this form differ from those of Spirographis i
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectreproduction, bookyea
