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. 



