JOURNAL OF ANIMAL BEHAVIOR 



Vol. 6 SEPTEMBER-OCTOBER No. 5 



REACTIONS OF PARAMOECIUM CAUDATUM TO 



LIGHT 



A. C. WALTON 



Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology at Harvard College. No. 279 



The experiments of Engelmann, Jennings, and Mast have 

 demonstrated that Paramoecium shows neither orienting nor 

 directive responses to light. Mast (1911, p. 134), who has 

 recently studied this question with care, makes the following 

 statement: "At noon on a perfectly clear day in July I ar- 

 ranged a double convex lens 10 cm. in diameter so as to focus 

 the direct rays from the sun on a slide under the microscope. 

 The light was passed through distilled water in order to cut 

 out the heat rays. The light at the focal point was at least 

 500,000 ca. m. in intensity. This extremely intense light was 

 repeatedly flashed upon the Paramoecia as they swam about 

 under the microscope, but there was no evidence of any re- 

 sponse whatever. It is altogether probable, then, that the 

 power to respond to light is not common to all protoplasm." 



The above statement and that of Engelmann, that Para- 

 moecium bursaria, a species containing chlorophyl, is positively 

 responsive to decreases of light intensities only when the oxygen 

 content of the water is below normal, have seemed to me to 

 allow further work along the line of intensity reactions in Para- 

 moecium.. The investigations of Hertel (1904) and of Oettli 

 (1910) have shown that Paramoecium is responsive to ultra- 

 violet rays and to heat rays. Why may it not react to visible 

 rays whose wave lengths are between those of ultra-violet and 

 heat? 



