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 A/datross 

 during deep-sea dredgings off the coast of Mexico. 

 This prawn {Benthesicymus tannert) 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 



