Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 PROTECTIVE MOVEMENTS 363 In many situations, however, these color changes may be protective, even though they are not necessarily protective adaptations in all cases. 408. Concealment. Another way in which an animal becomes invis- ible to its enemies is illustrated by the cuttlefish, which ejects a dark fluid into the water when it is pursued. This ' ink-bag ' trick clouds the water and thus enables the animal to escape from its pursuer. Fig. 181. The American
Elementary biology; an introduction to Elementary biology; an introduction to the science of life elementarybiolog00grue Year: 1924 PROTECTIVE MOVEMENTS 363 In many situations, however, these color changes may be protective, even though they are not necessarily protective adaptations in all cases. 408. Concealment. Another way in which an animal becomes invis- ible to its enemies is illustrated by the cuttlefish, which ejects a dark fluid into the water when it is pursued. This ' ink-bag ' trick clouds the water and thus enables the animal to escape from its pursuer. Fig. 181. The American chameleon The green Hzard {Anolis carolinensis). (From photograph by American Museum of Natural History) The instinct for finding shelter is very marked in many animals of nearly all classes. In many worms we may observe a strong tendency to crawl into cracks or angles. There are certain worms that are so persistent in this trait that if two of them are placed in opposite ends of a glass tube, they will approach each other and keep on driving forwards until they have worn their heads off. The contact of the body against the hard walls stimulates them to move forward, and they don't know enough to stop when they have gone far enough. A more remarkable home-finding instinct is that shown by the hermit crab, which makes itself at home in the discarded shells of snails. As the animal grows larger it abandons one shell and finds another (Fig. 182). With this instinct we may compare that of the higher animals that dwell in caves or other ready-made openings that they find.
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