i86 



LIGHT AND THE BEHAVIOR OF ORGANISMS 



solid rod several times as large as a single glower. It there- 

 fore cast a sharp shadow, a point of importance in the 

 following experiments. The time required to travel the dis- 

 tance was recorded just as under the preceding conditions. 

 The rate of movement was now obtained alternately under 

 the two conditions. The results appear in Table II. This 

 table shows that it required on an average 46.4 seconds to 



TABLE II 



travel 15 cm. in an Intensity of 7 ca. m., and 43.36 seconds 

 to travel the same distance in an intensity of 3888 ca. m. 

 Under the former conditions the larvae therefore crawled 

 at the rate of 0.321 cm. per second, and under the latter 

 at the rate of 0.345 cm. per second, a difference of only 

 0.024 cm. per second, due to a difference of 3881 ca. m. of 

 light. 



In studying the effect on the rate of locomotion of expos- 

 ing the posterior third and three-fourths of the larvae, the 

 apparatus was arranged just as described above. The time 

 required to travel 15 cm. in 7 ca. m. intensity was first 

 ascertained with a given larva, then the larva was trans- 

 ferred to the starting point, and after it had crossed the 

 thread a small beam of light 3888 ca. m. in intensity from 

 the three glowers was thrown on the posterior end and held 

 there by means of moving along by the side of the larva a 

 screen containing a small rectangular opening. The time 



