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C. F. CURTIS RILEY 



vessel was divided by transverse lines into three equal divisions 

 (see Fig. i, B). Toads found in the section marked + were 

 considered to respond positively to the light. Those gathered 

 in the division marked — were enumerated as responding nega- 

 tively. The organisms congregated in the space marked o were 

 counted as being indifferent to the illumination. Table I indi- 

 cates the results of six experiments with twelve individuals used 



in each experiment. 



TABLE I 



Responses of Young Toads to Weak Diffuse Daylight 



The above table shows that out of a total of 72 responses, 

 42 of them may be considered as being positive, 20 as being 

 negative, and 10 as being indifferent. The writer performed 

 many other experiments beside those indicated in Table I, some 

 of which showed a rather higher percentage of positive responses 

 than evidenced in the table ; but it is believed that the results 

 indicated there present a fairly representative series. From 

 these results the inference is drawn that young toads respond 

 positively to weak diffuse daylight. However, the orientation 

 of the animals lacks the definiteness exhibited in the experi- 

 ments with light of stronger intensities. Neither the motor 

 response nor the orientation is so precise as is the case in the 

 experiments with strong diffuse light. Many of the toads that 

 collected in the section marked + faced the slit-like opening in 

 the wall of the dark room through which the light entered. 

 Those toads that faced the light have the median longitudinal 

 axes of their bodies parallel with the longitudinal axis of the 

 experimentation dish and also parallel with a portion of the 

 incoming light rays. But it must be remembered that the 

 rays cross at many and varied angles, and while it is true that 



