362 WILLIAM H. COLE AND CARLETON F. DEAN 



the larva of Petroniyzon. The photokinesis of other animals 

 has been studied, the most recent report being that for Para- 

 mecimn by Walton ('16). The results of our experiments show 

 that frog tadpoles are sensitive to light during the mid-larval 

 stages, the reaction becoming a phototropic one just previous to 

 metamorphosis. 



We wish to express our sincere thanks to Prof. M. W. Eddy 

 for extending to us the privileges of the Zoological Laboratory 

 of the Pennsylvania State .College, and to Prof. G. H. Parker 

 of Harvard University for a careful reading and criticism of the 

 manuscript. 



All the tadpoles used were between 40 and 60 mm. long, a 

 stage later than that used by Laurens. A definite determina- 

 tion of the species was not made, but since all the adults found 

 :n the same pond where the tadpoles were taken, were Rana 

 clamitans, Latreille, it is very probable that the larvae were of 

 the same species. They were collected in the fall and kept in 

 large aquaria throughout the winter. As far as one could tell, 

 the animals remained in a normal condition, feeding on algae, 

 water cress and the remains of small Crustacea. Individuals 

 used in the tfials were kept in separate jars, so that repeated 

 trials could be made and compared. The results have been 

 grouped together, however, since the individual differences in 

 the reactions were small. 



APPARATUS AND PROCEDURE 



For the trials a blackened rectangular glass jar 260 by 200 by 

 150 mm. was used. It was partitioned longitudinally with a 

 blackened glass plate making the smaller section 50 mm. wide. 

 Light was admitted through a circular unblackened area at one 

 end on a level with the bottom. 



Light of three intensities was furnished by a small arc lamp 

 of 500 candle power, and two Spencer microscopic lamps, with 

 condensing lenses, of 100 and 48 candle power. The size of the 

 beam was controlled by slips of blackened cardboard containing 

 various sized openings. A blackened 8 candle power lamp, 

 giving just enough light to enable the observation of the animals' 



