NOTES. 423 



the development of the skin-pigment is influenced by light, even with 

 regard to man. 



Jfote 27,paffe '.t2. Heincke describes the colours of Gobius Rvthemt- 

 parri as follows : ' In the first instance a black velvety spot is conspicuous 

 lying at the base of the caudal fin and surrounded by a beautiful golden- 

 yellow margin. A similar black spot, but without any yellow rim, is 

 found in the male, on each side, at the base of the pectoral fin ; this is 

 absent in the female. The ground-colour of the back of the male 

 is, in the breeding season, of a dark brownish black, cutting in on the 

 green j on the head it is lighter with a reddish tinge ; there are five 

 light-coloured saddle-shaped spots with a metallic sheen, and the under- 

 surface of the head is of a vivid copper-colour with a golden gleam. 

 On each side, between the light and dark colour of the body, and rather 

 below the lateral line, there is a row of vivid spots as bright as jewels, 

 glittering now blue, now green, and there is a similar spot on each gill- 

 covering, which is otherwise red. The two doisal, the caudal and the 

 anal fins are cherry colour and yellow, or show green stripes and bands 

 on a dark ground. The pupil of the eye shines a deep blue.' To this 

 somewhat abridged description he adds : ' I have given these elaborate 

 details that the reader may form some idea of the beauty of the Gohius 

 at certain moments, for all this gorgeous colouring may vanish within a 

 short time and not return in its pristine splendour for a long time.' He 

 then fully describes the chromatophores and their function. 



Note 28, page 97. Dewar, ' The Physiological Action of Light,' 

 Nature, 1877, p. 433. 



Note 2^, page 99. Darwin himself frequently uses the word ' colour ' 

 where ' distribution of colours ' or ' mode of colouring ' would be better. 

 Still it is always clear from the context that he attributes to origin 

 through Sexual Selection only such variations in colour as occur for in- 

 stance in the male and female of the same species, and to Natural 

 Selection such as have proved a protection, and therefore advanttigeous 

 to animals. To assume colouring, i.e. the determined mode and arrange- 

 ment of colour, is to assume the pre-existenoe of colour ; the question as to 

 how this originated has never, to my knowledge, been inquired into in 

 these later times, and perhaps it is for this very reason that it has fre- 

 quently been confounded with the origin of the mode of its distribution. 

 (Compare Darwin, Desoent of Man, chap, on Sexual Selection.) Other 

 naturalists, at any rate, have certainly made this confusion. Thus, for 

 instance, the variation of green to brown which is exhibited by many 

 Sphinx-caterpillars has been attributed to natural selection (see Weis- 

 mann, Studien atir Desoendenz-Theorie. Die Mititelmng der ZtAclmwng 

 bei den Soh/metterlingsraiipeti, p. 80). Selection, however, could not 

 possibly effect any alteration in the pigment, but could only operate 

 after such a change had actually occurred. 



Note 30, page 100. There are many works, not here referred to, on 



