122 COLOUR IN NATURE chap. 



red cells. Only about 3 per cent had red spots on 

 the shells. 



At the beginning of August the red spots on the 

 shell had completely disappeared, but the blue colour 

 with the two red patches still persisted. By the middle 

 of August the great majority of the individuals had 

 lost their bright colours, and by September the 

 minority was very much smaller. The few which 

 still retained any colour had the abdominal stripes of 

 a greenish-blue, with greenish spots at the bases of 

 the legs, at points which had previously been red. 

 The red spots on the shells in the early stage con- 

 sisted of red and blue cells intermixed. According 

 to Fritsch there is no reason to suppose that the 

 " decorative colours " have any sexual significance. 



This description shows very clearly how often 

 blue and red colours are locked together, and how 

 red may disappear to be replaced by blue or green. 

 Quite similarly Dr. F. H. Herrick, in describing the 

 development of the American lobster, notes the 

 striking colour-variations among individuals, some 

 "being bright red, others greenish-blue, and others 

 pale blue or nearly colourless." 



Illustrations of this relation between red and blue 

 might be multiplied to any extent, and yet it should 

 also be noted that there is not infrequently much 

 constancy of coloration, at least in detail. The lower 

 surface of the penultimate segment of the chelse in 

 Astacus nobilis is always a bright orange-red, although 

 the tints of the other parts of the body may show 

 considerable variation. Those who are in the habit 

 of dissecting Nephrops norwegicus must have been 

 struck by the constant bright red colour of the gullet. 



