AND OF LIGHT. 255 



phosphorescent creatures is capable of taking the place 

 of sunlight in those depths which the rays of the sun 

 cannot penetrate." * 



The more striking and considerable effects produced 

 by light in members of the Animal Kingdom are mostly 

 confined to cases of so-called " Variable Protective and 

 Aggressive Resemblance," or reaction to the colour of 

 the surroundings which either protects the animals 

 from their enemies, or assists them to capture their 

 prey.f Such a reaction is rarely, if ever, a direct re- 

 sponse to light of the superficial tissue cells as a whole, 

 or even of the sensitive pigment cells in the skin which 

 have been gradually formed in the course of evolution 

 through the agency of Natural Selection and other 

 processes. It is an indirect effect produced by the in- 

 termediation of the nervous system. This was first 

 proved to be the case by Briicke for the chameleon, 

 and by von Wittich for the frog. The latter observer 

 regarded the variations in colour as probably reflex in 

 their nature, he attributing them to a peripheral gan- 

 glionic apparatus in the skin itself. A few years later 

 Lord Lister | took up the problem and correctly solved 

 it, he concluding that in Rana temporaries " the eyes are 

 the only channels through which the rays of light gain 

 access to the nervous system so as to induce changes of 

 colour in the skin." The very conspicuous changes 

 which can be produced in this manner may be illus- 



* Quoted from Semper 's "Animal Life," p. 85. 

 f Vide Poulton's " Colours of Animals," pp. 81 to 158. 

 tlV. Bd, d. mathemat. naturwiss., Classed. Kaiserl. Acad. d. 

 Wissenschaft, Wien, 1852. 

 Muller's Archiv. 1854, p. 41. 

 H Phil. Trans. 1858, p. 627. 



