THE IMPENETRABLE SEA 



appropriately blue-blooded, due to the presence of a 

 copper-containing compound in their blood which 

 causes the colour, even as the characteristic colour of 

 man's blood is caused by the presence of the iron com- 

 pound haemoglobin in the red corpuscles [erythrocytes) : 

 five millions of them in every cubic centimetre of the 

 fluid. Man's red blood corpuscles are individually a 

 pale greenish-yellow, but in dense masses, the erythro- 

 cytes colour changes to a distinct red, even as cephalo- 

 podan blood is a pale clear blue when deoxygenated and 

 a rich dark blue when oxygenated. 



Squids are the most colourful of all cephalopods in 

 more ways than one. The bodies of some species are 

 covered with numbers of tiny pigment spots. When ex- 

 panded at the will of the squid, by the use of numbers of 

 microscopic, fast-acting muscles, the animal is given its 

 characteristic colour. But when the squid wants to make 

 itself inconspicuous it can use the muscles to contract 

 the pigment spots, with the result that the creature 

 virtually disappears from view without moving. 



Although less efficient than that of the common cuttle- 

 fish, the squid's skin-mechanism outdoes the chameleon's 

 in the rapidity of its colour changes. The vanishing trick 

 just described is one of the two methods which the squid 

 uses to elude its enemies. The other is well known, but 

 seldom fully understood : its swift use of jet-propulsion. 



Squids are masters of this vanishing trick — they draw 

 water into their body chambers, which are lined with 

 powerfully-muscled walls. Suddenly, the water is ex- 

 pelled so violently that the escaping stream makes the 

 squid's body shoot backward. This is one of the squid's 

 normal modes of progression, but if it wants to escape 

 from danger it can release a stream of blinding ink. This 

 extraordinary fluid is discussed at considerable length in 

 Frank W. Lane's authoritative and invaluable work 

 Kingdom of the Octopus,"^ the flrst book on the octopus and 



♦Jarrolds, London. 1957. 



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