Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 352 ELEMENTARY BIOLOGY In certain experiments with flatfish that are ordinarily pig- mented on the upper surface and white on the lower surface, the light was supplied from below by means of mirrors, with the result that the fish developed pigments on the lower sur- face and remained white above. From these experiments and from our own experience with getting tanned, we may feel con- fident that at least in many cases the formation of the pigment is due to the st
Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 352 ELEMENTARY BIOLOGY In certain experiments with flatfish that are ordinarily pig- mented on the upper surface and white on the lower surface, the light was supplied from below by means of mirrors, with the result that the fish developed pigments on the lower sur- face and remained white above. From these experiments and from our own experience with getting tanned, we may feel con- fident that at least in many cases the formation of the pigment is due to the stimulation of the light. But we know also that there are many other pigments that are formed without refer- ence to the light, whether they have any protective value or not. 401. Invisibility. In relation to enemies that can sec, one of the most obvious means of protec- tion is something to make one in- visible. The jellyfish (Figs, 154, a, and 155, <^) is so nearly transpar- ent that it is practically invisible in the water. But transparency is not the only means by which an object may be made invisible. The see- ing of objects depends upon the contrasts in lights and shadows ; an object that is colored like the background becomes by that fact invisible. This type of invisibility is so common in nature that some men claim to be abie to tell the kind of surroundings an animal naturally occupies from the character of its surface colorings. The green katydid among the green leaves is a common example of so-called protective coloration Fig. 168. The underwing moth (Catoca/a). (Shghtly reduced) When they are at rest, the moths of this genus resemble the bark of trees, so that they are no doubt often over- looked by their enemies
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