THE VOYAGE OF THE BEAGLE 17 



acrid secretion, which is spread over its body, causes a 

 sharp, stinging sensation, similar to that produced by the 

 Physalia, or Portuguese man-of-war. 



I v/as much interested, on several occasions, by watching 

 the habits of an Octopus, or cuttle-fish. Although common 

 in the pools of water left by the retiring tide, these animals 

 were not easily caught. By means of their long arms and 

 suckers, they could drag their bodies into very narrow crev- 

 ices; and when thus fixed, it required great force to remove 

 them. At other times they darted tail first, with the rapidity 

 of an arrow, from one side of the pool to the other, at the 

 same instant discolouring the water with a dark chestnut- 

 brown ink. These animals also escape detection by a very 

 extraordinary, chameleon-like power of changing their col- 

 our. They appear to vary their tints according to the nature 

 of the ground over which they pass : when in deep water, 

 their general shade was brownish purple, but when placed on 

 the land, or in shallow water, this dark tint changed into one 

 of a yellowish green. The colour, examined more carefully, 

 was a French grey, with numerous minute spots of bright 

 yellow: the former of these varied in intensity; the latter 

 entirely disappeared and appeared again by turns. These 

 changes were effected in such a manner, that clouds, varying 

 in tint between a hyacinth red and a chestnut-brown, 4 were 

 continually passing over the body. Any part, being subjected 

 to a slight shock of galvanism, became almost black: a simi- 

 lar effect, but in a less degree, was produced by scratching 

 the skin with a needle. These clouds, or blushes as they may 

 be called, are said to be produced by the alternate expansion 

 and contraction of minute vesicles containing variously 

 coloured fluids. 5 



This cuttle-fish displayed its chameleon-like power both 

 during the act of swimming and whilst remaining stationary 

 at the bottom. I was much amused by the various arts to 

 escape detection used by one individual, which seemed fully 

 aware that I was watching it. Remaining for a time motion- 

 less, it would then stealthily advance an inch or two, like a 

 cat after a mouse; sometimes changing its colour: it thus 



* So named according to Patrick Symes's nomenclature. 



B See Encyclop. of Anat. and Physiol., article Cephalopoda. 



