512 THE BIOLOGY OF MARINE ANIMALS 



chromatophore in Sepia occurs in two-thirds of a second (Fig. 12.4) (31). 

 Such sweeping alterations in tones and colours have cryptic value in 

 breaking up the animal's outline, and assist it when darting upon its prey 

 or evading a predator. Holmes (35), who has made a study of colour 

 changes in the cuttlefish Sepia officinalis, finds that this animal has a 

 definite series of patterns which are exactly repeated under suitable condi- 

 tions (Fig. 1 1.12). These involve a zebra pattern in actively swimming ani- 

 mals over light sandy bottoms; a light mottled pattern when the animal 



Fig. 12.4. Chromatophore Responses est an Isolated Piece of Skin 

 from Sepia, Recorded by Photocell and Rapid Galvanometer 



(a) Single twitches, resulting from electrical stimuli at 45/min; (b) single twitches, 

 partial summation at about 90/min; (c) nearly complete summation at 9-3 shocks/sec. 

 Time marks i sec. (From Hill and Solandt (31).) 



is at rest on sandy bottoms ; very dark and extremely pale appearances on 

 black or white backgrounds ; and highly contrasted black and white pat- 

 terns on a black and white background. 



When hunting or when disturbed, the cuttlefish shows a whole series of 

 remarkable colour transformations which follow one another in regular 

 succession. Holmes writes (p. 27) — 



If further irritated the animal may respond by a total paling of the whole of its 

 body, and upon this background may appear longitudinal black stripes, at the base 

 of the fins and along the middle of the back. These lines flicker vividly over the 

 pallid back, and then suddenly disappear, to be followed perhaps by a reappearance 

 of the black spots, another total darkening, or a brief reappearance of the zebra 

 pattern. All this time the animal darts about rapidly, as if to avoid the irritation, and 

 its final action when it cannot do so is to eject a cloud of ink. Then at once it 

 becomes motionless, and hides behind the black cloud which it has produced, and 

 its colour can be observed no more. 



Some cephalopods can also adapt themselves very well to the colour of 

 their background when at rest. On a green background Sepia assumes a 

 greenish tint: the orange chromatophores are contracted, and the black 

 and yellow chromatophores, interacting with some green reflexion from 

 the underlying iridophores, produce a greenish tint. On a yellow or red 

 background the expanded yellow and red chromatophores exclude the 

 iridophore layer. Different shades of grey are due to altered states of the 

 black chromatophores, which expand or contract according to the neutral 



