i84 



LIGHT AND THE BEHAVIOR OF ORGANISMS 



the anterior end there are two minute cone-shaped pro- 

 tuberances not over 0.5 mm. apart (Fig. 30). These pro- 

 tuberances can barely be seen with the naked eye when 

 the anterior end is extended, and not at all when it is con- 

 tracted. Judging from their connection with the nervous 

 system, I am inclined to believe that they are light recipient 

 organs. 



a.sp 



D 



I I I I 

 5 mm^ > 



Fig. 30. Musca larva. A, side view anterior end expanded; a.sp., anterior 

 spiracular process showing seven spiracular papillae; o.t, optic tubercle. After 

 Hewitt (1908, PL 30, Fig. g). B, camera outline, dorsal view showing anterior 

 end expanded. C, same showing anterior end contracted, and optic tubercle 

 withdrawn and turned under as it is during the process of looping. D, dorsal 

 view of entire animal. 



g. Effect of light intensity on rate of locomotion. — The 

 effect of light intensity on the rate of locomotion in fly 

 larvae was tested under three conditions: (i) with the entire 

 larva exposed; (2) with the posterior third exposed; and 

 (3) with the posterior three-fourths exposed. 



h. Method. — A glass plate 25 cm. square was covered 

 with two sheets of filter paper over which was placed a 

 sheet of smooth black paper. This was then thoroughly 



