90 STUDIES IN LIFE AND SENSE. 



New forms they take, and wear a borrowed dress, 



Mock the true stone and colours well express ; 



As the rock looks, they take a different stain, 



Dapple with grey, or mock the livid vein ; 



Thus they, concealed, the dreaded danger shun, 



By borrowed shapes obscured, and lost in seeming stone. 



So, also, another classic writes 



Remark the tricks of that most wary polypus, 

 Which always seems of the same colour and hue 

 As is the rock on which he rests. 



The assimilation of an animal's colour to the surfaces on which 

 it rests forms a notable circumstance of zoology, which has been de- 

 nominated "mimicry." Under this head are included all phenomena 

 which enable an animal to assume the form, likeness, or colour of 

 another animal, of a plant, or of an inorganic object. That cuttle- 

 fishes possess such a power is well known. The hue of an octopus 

 may so closely resemble that of the rock to which it attaches itself, 

 that the observer can "with difficulty say which is rock and which is 

 animal. A flounder's colour is in the same way assimilated to the 

 sand on which it rests, although in the fish the alteration of colour 

 seen in the cuttlefishes is not represented. 



The manner of production of the changes of hue and play of 

 " shot " colours in the cuttlefishes is really analogous to that whereby 

 the famed chameleons effect their alterations of hue. Beneath the 

 thin and transparent cuticle or outer integument, and embedded in 

 the dermis or under-skin itself, lie certain contractile colour-cells 

 which receive the name of chromatophores. These, by alteration of 

 their granular colour-granules under the stimulation of light or imita- 

 tion, produce the changes of hue. Rapid diffusion and extension of 

 these cells will produce the appearance of the diffused play of colour 

 so familiarly seen in these animals, whilst certain highly refractive 

 corpuscles, named Flitterchen by German physiologists, aid in pro- 

 ducing the shot colours, by light-interference. It is interesting to 

 note that in the common frog changes of colour are perceptible in 

 the skin, and are effected by analogous methods to those which pro- 

 duce the variations in hue of the cuttlefishes. Thus the pigment-cells 

 of the frog's skin contract under the stimulus of light, their colour- 

 granules are huddled into the centre of the cell, and the skin becomes 

 blanched. When the stimulus is removed, the pigment-cell ex- 

 pands, its granules are diffused, and the frog's skin resumes its normal 

 coloration. It is noteworthy that in groups of animals so distinct as 

 those just mentioned, one should find closely allied means for attaining 

 a similar end. This remark holds good of other structures in cuttle- 

 fishes, which, although of independent origin, subserve functions allied 

 to those performed by the structures and organs of Vertebrata. 



The locomotion of the cuttlefishes forms a point of interest in 



