360 WILLIAM H. COLE 



was used, the observations being made with a Spencer binocular 

 microscope. 



The following series of experiments were performed: 



1. LN series (64 cases): Transplants over normal eyes of ani- 

 mals kept in the light. 



2. DN series (16 cases) : Transplants over normal eyes of 

 animals kept in darkness. 



3. LO series (13 cases) : Transplants o\-er eyes whose optic 

 nerves had been cut; or over the sockets after the eyes had been 

 removed. Animals kept in the light. 



4. LB series (71 cases) : Transplants on the body region of 

 animals kept in the light. 



5. LBE series (15 cases) : Transplants over 'artificial eyes' on 

 the body region of animals kept in the Ught. 



6. DBE series (9 cases): Transplants like the LBE series; the 

 animals kept in darkness. 



7. LT series (13 cases) : Transplants on the tail region of ani- 

 mals kept in the light. 



The source of the transplants varied in the individual cases, 

 as will be seen by referring to the tables wliich follow. 



GENERAL OBSERVATIONS 



1. Pigmentation 



Among the stock animals there was very little difference in 

 pigmentation of the integument from day to day. All of them 

 were brown, varying from a light to a very dark shade. The 

 animals used in the experiments, however, often showed great 

 differences, ranging from complete expansion to complete con- 

 traction of the melanophores, depending on the conditions of 

 their environment. To investigate the causes of such changes 

 in pigmentation, tadpoles were exposed to varying conditions of 

 temperature, illumination, and oxj^gen supply. It was found 

 that, independently of ordinary illumination, a low temperature 

 causes an expansion of the melanophores. Animals whose me- 

 lanophores were maximally contracted were put into water at a 

 temperature of 0°C., and exposed to diffuse daylight. After 



