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 chelae 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, 
