CHAP. X GENERAL BIOLOGY 669 



The close correspondence between the development of 

 pigment and the vertical distribution is very striking. Nos, 

 I and 2 live above 150 metres, and are nearly transparent. 

 Nos. 3 to 7 are distinguished by deep red colours with blue 

 patches, and were taken above 500 metres during the night, 

 iDut in the daytime have their maximum distribution at 500 

 metres or deeper. Nos. 8 to 1 1 have no blue pigment, but 

 only red and yellow colours, and live deeper than 500 metres, 

 not having been taken in less depths even at night. 



As indicated in Chapter IX. the deep layers contain a great Dark-coloured 

 variety of animals, and in all these groups we repeatedly find jee^^gr kVrs^ 

 the same dark colours. In the medusae Atolla, Periphylla, 

 Crossota we find dark-brown colours or, as in Agliscra and 

 others, red colouring. Among the Sagittidae we meet red 

 colours [Sagitta macrocephala, Ezikrohnia fowleri). All the 

 crustaceans are red [Buchtrta, Cyclocaris, Gigantocypris, Schizo- 

 poda, Decapoda) ; in the Pteropoda the colours are dark violet 

 {Pe7^aclis diversa, Limacina helicoides, Cliofalcatd). The squids 

 are red, the fishes black or blackish violet. 



In the Atlantic gray, mirror-like, and silvery colours are Silvery and 

 characteristic of the fishes between 150 and 500 metres. The 

 silvery sheen is very often iridescent with dark green, shallower 

 violet, and blue tinges (see Argyropelectis affinis in Plate II.). ^^^^"^^^ 

 The backs of these animals are brown or black. 

 These colours correspond to those of the herring in boreal 

 waters, and as previously mentioned they have been well 

 known and recognized as protective colours. From above 

 the fish are not easily seen because from this point of view 

 the ocean looks dark or black. On the other hand, the light 

 rays from above are reflected by the mirror-like sides of the 

 body. From a position below the fish an eye would have great 

 difficulty in distinguishing the outlines of the fish because of the 

 rays coming directly from the source of light. This can only 

 be understood when examining the fish in a living condition, 

 for preserved fishes lose their silvery sheen very soon, generally 

 turning black, and losing their original appearance. Most 

 Scopelidae have generally been represented as black, but many 

 of them are really quite silvery (see Fig. 491, which, however, 

 is not very good, because the silvery sheen does not come out 

 well in this kind of reproduction). 



These remarks apply not only to the animals of this inter- 

 mediate layer, but to many surface forms having a similar 

 arrangement of colour. During our Atlantic cruise this was 



light-coloured 

 animals in the 



