672 DEPTHS OF THE OCEAN chap. 



sunlight disappear, viz. Chwicera mirabilis and Alacrurus cequalis. 

 Brown, blue, and violet are the principal colours of the abyssal 

 fishes ; very often the pupil of the eye is yellow, as in Chim^era. 

 But has any eye at all the power of perceiving colours in the 

 abyssal region? Is any other light present there than the light 

 produced by the animals themselves ? 



In what has been said above I have compared the 

 conditions of light and the colours of animals at various depths, 

 and in every case we have had to acknowledge that there is 

 some connection between the colours of the fauna and the 

 light-intensity in the surrounding water. On the other hand it 

 is in many cases difficult to show that the colours are actually 

 protective colours, and many scientists have relinquished the 

 idea that the colours are protective. The indisputable 

 connection between light-intensity and peculiarities of colouring 

 has been explained as resulting from a purely physiological 

 process of assimilation. An interesting attempt in this 

 Pigmentation ^ direction has been made by Doflein,^ who says : " In normal life 

 certain gland-shaped organs in the higher decapod Crustacea 

 form pigments. The formation of these pigments is influenced 

 by light. Feeble light is sufficient for the formation of red 

 pigment. Under the influence of light and of still unknown 

 processes of assimilation, the red pigment may be transformed 

 into yellow or even into white pigment. Very little is known of 

 the nature of the yellow and white colour substances, which may 

 perhaps arise from a union of the pigment and other con- 

 stituents of the body of the crustacean, for instance, the lime 

 salts. The blue pigment is derived from the red under the 

 influence of light, and dissolving passes into the tissues where 

 it becomes colourless and disappears, evidently through the 

 chemical processes into which it enters. The destruction of 

 blue pigment occurs also under the influence of light, this 

 substance thus being of a temporary nature, visible only 

 when produced in great quantities, but under other conditions 

 destroyed as soon as formed. This would explain the presence 

 of red pigment in crustaceans living in deep water, and the 

 lack of pigment in many pelagic Crustacea, as well as the blue 

 colours of oceanic forms. In the surface layers of the ocean 

 the formation and destruction of pigment, under the influence of 

 light, are in equilibrium. Small quantities of pigment indeed 

 prove to be present in nearly transparent forms, but in the 



^ F. Doflein, " Lcbensgewohnheiten und Anpassungen bei Decapoden Krebsen," Festschrift 

 fa r Richard Hertwig, Bd. iii. , Jena, 19 lO. 



