Curious Creatures 20 1 



chromatophore, like an enlarging freckle, spreads out 

 until it coalesces with its neighbor. These changes — 

 from white to deep mottled brown or full purple, or the 

 reverse — can be produced instantly and can be re- 

 stricted to different areas of the body, thus enabling it 

 to simulate a pebbly bottom or other environment with 

 more or less fidelity. Few things are more startling to 

 the novice than the rapid flashes of color that pass 

 over these creatures. At one moment it may be of a 

 deep tone contrasting strongly with some shell-covered 

 floor, then suddenly it becomes almost invisible by turn- 

 ing a ghostly white, and will slink away like a specter 

 of its former self. The mode of progression used by 

 the squid is no less curious than its appearance. Its 

 body may roughly be compared to a common force 

 pump wherein water enters at one aperture and is ex- 

 pelled at another. It is the force of the water directed 

 through the "spout," or siphon, located just below the 

 head at the base of the tentacles, that propels the ani- 

 mal. This force is produced by contractions of the 

 mantle, a loose saclike envelope wherein are enclosed 

 the stomach and other vital organs. Usually the squid 

 swims with its so-called tail foremost, but it can reverse 

 its course without changing the direction of its body 

 simply by turning its flexible siphon the opposite way. 

 In addition to their effective color changes, all ceph- 

 alopods, with the exception of the single genus Nauti- 

 lus, possess a unique organ, called the ink bag, with 

 which they can render themselves invisible. This organ 

 produces an effect similar to the smoke screen employed 

 by naval vessels in combat. When one of these animals 

 is irritated or pursued, it ejects a black substance 



