120 
COLOUR IN NATURE 
CHAP. 
chromatophores only. This case is exceedingly 
curious, but is confirmed in a striking manner by an 
observation made on a prawn taken by the Albatross 
during deep-sea dredgings off the coast of Mexico. 
This prawn (Benthesicymus tanneri ) is usually of a 
deep blood-red or crimson colour. In one specimen, 
however, the abdomen was marked with spots of 
blue on the second, third, and fourth abdominal 
segments. The spot on the second segment was 
partly blue and partly yellow, the line of demarcation 
between the two colours crossing the segment 
obliquely so as to produce a strikingly unsymmetrical 
type of coloration. In view of Pouchet’s observations 
mentioned above, Mr. Faxon in describing the 
Crustacea of the Albatross suggests, reasonably 
enough, that this peculiar appearance is due to a 
change induced during the passage from the ocean 
depths to the surface. This suggestion leads on to 
the curious fact that the blue and green pigments 
are almost invariably absent from deep-sea Crustacea, 
which are usually shades of red, often deep red, or 
pink, but occasionally yellow or dead-white. When 
blue or green colours occur they are almost always 
confined to the eggs. As might be expected, many 
have sought to explain this fact as due directly to 
the absence of light at great depths. Without 
entering at this stage into details on the subject, it 
may be noted that such facts as that the fresh-water 
crayfish occasionally appears in a full blue or in a 
red variety, that the common lobster is sometimes 
red in the living condition, that in Copepoda living 
under similar conditions the eggs are sometimes red 
and sometimes blue, and so on, suggest that the 
