REACTIONS OF AMPHIBIAN LARVAE TO LIGHT 



201 



no need to do so again here. It has also been shown that the 

 phototactic reactions of amphibia when the skin alone is illumi- 

 nated are apparently not due to the direct stimulation of the cen- 

 tral nervous system by light. Parker ('03) has shown this in 

 the case of the frog, while Dubois ('90) on Proteus, and Reese 

 ('06) on Cryptobranchus and Necturus have done the same for 

 these animals. Amblystoma larvae are, of course, much smaller 

 and more transparent than the adult forms which these investi- 

 gators used, and the chances that the light, penetrating the mus- 

 cles, might directly stimulate the central nervous system are 

 much greater. But further series of experiments bring additional 

 evidence that here again the reactions are not due to the direct 

 stimulation of the central nervous system. In these experiments 

 the testing dish was placed at a distance of 25 cm. from the light, 



TABLE 2 

 Reactions of normal Amblystoma larvae to local skin illumination 



REACTIONS 



Directions of 



Number of responses. 

 Per cent of responses 



REGIONS ILLUMINATED 



Head 



+ 



123 



62 



Mid-body 



TaU 



+ 



107 

 54 



110 

 55 







27 

 13 



where its intensity was about 768 candle-meters. The beam of 

 light was made to pass through a small opening in a screen placed 

 close to the glass dish. In this way a small area of a larva could 

 be illuminated. A series of tests were made on ten normal and 

 on ten blinded larvae, in which different small areas were illu- 

 minated. Three regions were selected which may roughly be 

 described as the head region, the ventro-lateral mid-body region, 

 and the tail region. Fifteen minutes was the time allowed for 

 the responses. The results of .these tests are given in tables 2 

 and 3. As may be seen, positive responses were obtained when 

 each of the three regions in both normal and eyeless larvae were 

 exposed to the light. A simple turning of the anterior end of the 

 body toward or away from the light was taken as a positive or 

 negative response. The beam of light was, of course, so small. 



