PHOTOKINETIC REACTIONS OF FROG TADPOLES 309 



intensify the photokinetic response, we conclude that the state 

 of contraction or expansion does not affect primarily the reac- 

 tion to photic stimulation. The light adapted animals showed 

 almost the same per cent of activity as normal animals, which 

 gives further proof that the reaction is probably due to a nervous 

 mechanism and not to direct irritability of the melanophores. 



SUMMARY 



1. Frog tadpoles of Rana clamitans, Latreille, are sensitive to 

 light when a length of at least 40 mm. or more is attained. 



2. The skin is the important receptor for photic stimulation, 

 the tail region being the most sensitive. 



3. The reaction to photic stimulation varies with the age or 

 stage of development of the tadpoles; the youngest stages being 

 indifferent, the midlarval stages being photokinetic, and the 

 final stages being positively phototropic. 



4. Light and dark adaptation have very little influence on the 

 intensity of the reaction. 



5. The reaction is probably controlled by a nervous mechanism 

 and not by direct stimulation of the melanophores. 



LITERATURE CITED 



Babak, E. 1910 Zur chromatischen Hautfunktion der Amphibien. Pflliger's 



Archiv, Bd. 131, S. 87-118. 

 Banta, a. M. and McAtee, W. L. 1906 The life-history of the cave salamander, 



Sperlerpes maculicaudus, Cope. Proc. U. S. Nat. Mus., vol. 30, pp. 



67-83. 

 Eycleshymer, a. C. 1908 The reactions to light of the decapitated young 



necturus. Jour. Comp. Neur., vol. 18, pp. 303-308. 

 Franz, V. 1910 Uber die Bedingungen der Phototaxis bei freibeweglichen 



Tieren. Centralbl. f. Physiol., Bd. 24, S. 833-837. 



1913 Die phototaktischen Erscheinungen im Tierreiche und ihre 

 RoUe im Freileben der Tieren. Zool. Jahrb. (Abt. f. allg. Zool. u 

 Physiol.), Bd. 33, S. 259-286. 



Laurens, H. 1911 The reactions of Amphibians to monochromatic lights of 

 equal intensity. Bull. Mus. Comp. Zool., vol. 52, pp. 253-302. 



1914 The reactions of normal and eyeless amphibians to light. Jour. 

 Exp. Zool., vol. 16, pp. 195-210. 



1915 The reactions of the melanophores of Amblystoma larvae. Jour. 

 Exp. Zool., vol. 18, pp. 577-6.38. 



