50 DEVELOPMENT AISTD HEREDITY. 



colour of the light thus admitted to act in the inte- 

 rior of the tissues of the body, is dependent on the 

 colour reflected by the environment of the animal, 

 and also on the colour absorbed or turned back by 

 the skin. If a brown or yellow colour should be 

 everywhere reflected on an animal by its environ- 

 ment, this colour would preponderate in the light 

 which entered the body, perhaps to the disadvan- 

 tage of the animal's internal physiological func- 

 tions ; but since in such cases the same colour is 

 reflected back by the pigments of the animal, there 

 would thus be a tendency to restore the normal 

 balance of white light, which is most favourable 

 to organic functions. Living matter seems to be 

 in a general way capable to a certain extent of 

 photographing colours when exposed for many gen- 

 erations. An example is found in the fishes, crabs, 

 shrimps, worms, polyzoa, and hydroids, which live 

 among the masses of yellow sea-weed found float- 

 ing in the Gulf Stream, and which all partake of 

 the yellow colour of the weed. Another instance 

 is that of the animals of the great Sahara desert, 

 all of which, both those preying and those preyed 

 upon, share alike the tawny colour of the desert. 

 The fact that the colouration of animals increases 

 toward the equator leads easily to the supposition 

 that the lack of pigment or whiteness of animals 



