Camouflage 195 



substance from these diffusing into the fluids of the 

 body and giving the animal a transparent tint of deli- 

 cate blue. As this is a phase which under natural con- 

 ditions is assumed at nighttime, it is interesting to note 

 that chromatophores of prawns kept in the dark con- 

 tinue for several days periodically to expand and con- 

 tract, the rhythmic movements of the pigments being 

 regulated in a manner corresponding to the alternation 

 of day and night. 



The habit of hiding involves none of the freatures of 

 camouflage that w^e have considered, but it is apparent 

 that the safety from attack which weak animals find in 

 this form of protection is of considerable consequence 

 in their struggle for existence. Very early in my con- 

 tact with seashore life the significance of this method 

 of concealment was strongly impressed upon me. The 

 incident which I have in mind beside revealing animal 

 behavior, introduced me to that very curious creature, 

 the squid, an animal hitherto known to me only through 

 pictures and writings. 



At that time I was quite unfamiliar wath many of the 

 tide-pool inhabitants, and the most commonplace of 

 them would hold my wondering attention for hours. 

 A periwinkle making its way over a frond of seaweed, 

 a little horseshoe crab plowing through the mud or a 

 sea worm slowly extending itself out of the slime, were 

 novel and thrilling affairs. A circumstance, too, of no 

 mean magnitude was the molting of a crustacean. Now, 

 a lady crab, in the slow process of shedding its skin, 

 had once engaged my curiosity for a considerable 

 while when eventually I realized by the rising water 

 that the incoming tide had reached the pool and that 



