422 NOTES. 



Specimens which I kept for a year and a half in white vess Is, ar.d as 

 close as possible to a window with white blinds, assumed a very light 

 yellow-green colour in which a very few scattered specks of black 

 pigment could be detected ; but the small silvery spots which sometimes 

 appear on these creatures when about six months old attained so large 

 a size, particularly on the tail, that the animal might be described as 

 yellow-green with silver spots ; in some cases the silver spots predo- 

 minated. In young specimens of this year's brood, which were also 

 from the first reared in a diffused white light, the green colour is already 

 beginning to show, and the silver spots also on the larger specimens on 

 the face of the external branchiae. (This is in August; the young 

 Axolotl are about 50 days old, and the larger-sized ones about 7 cent, 

 long.) These results of my experiments agree tolerably well with 

 those of Pouchet and Lister if we assume that the colouring of the 

 Axolotl is produced entirely by the action of chromatophores. The 

 black pigment and the silvery hue, at any rate, appear to reside in such 

 cells, but the pale yellow-green ground hue of the specimens kept in a 

 white light appears to result from a pigment distributed and diffused 

 throughout all the organs. Hence any pronounced adaptation of 

 colouring to the surrounding objects such as occurs among fishes and 

 crustaceans is certainly not in question, and nevertheless the whiter 

 light induces paler colouring. 



The pigment of butterflies of which the pupae lie buried in tbe 

 earth is developed in total or almost total darkness before they escape ; 

 the chitinous skin of many pupae (of moths, &c.) is so dark as to be 

 almost perfectly impenetrable to light ; nevertheless pigment of very 

 various characters developes in them. We may, indeed, presume that in 

 most viviparous animals the development of the embryo takes place in 

 total darkness ; nevertheless they are all born with bright colours. Here 

 too must be mentioned the observation made by Kerbert that in the 

 embryo of the chick certain pigment cells which appear in the cutis 

 about the fifteenth day have wholly disappeared by the twenty-third. 

 It may be supposed that not much light, or none indeed, can penetrate 

 to the embryo through the egg-shell and membranes ; nevertheless, 

 pigment cells are formed and disappear again during the course of 

 the embryo stage. No explanation of this remarkable circumstance 

 has as yet been given. It is not uncommonly supposed that the pre- 

 sence of a dark pigment in the skin of human beings is due to the 

 greater intensity of light, as proved by the predominance of dark 

 races of men towards the equator and by the darkening of the skin 

 in summer. As, however, no experiments are before us by which the 

 chemical or heat rays have been excluded from acting on the skin at 

 the same time as the light rays, while the action of the air and that 

 of difference of nourishment have remained disregarded, we cannot 

 consider the conclusion as proved, or even admissible, which asserts that 



