196 HENRY LAURENS 



which he has called a 'Fluchtbewegung/ caused by the abnor- 

 mal conditions under which the animals find themselves. 



My experiments were carried on in a basement dark-room, the 

 temperature of which varied between 15° and 19°C. A 60-watt 

 Mazda lamp on a 110-volt circuit was used as the source of light. 

 This was placed in a wooden box, in one end of which there was 

 an opening 8 cm. square, through which the light was projected. 

 The larvae whose reactions were to be tested were placed singly 

 in a flat cylindrical glass dish, of 22 cm. diameter, and 8 cm. deep, 

 holding 2500 cc. of water. The sides and bottom of the dish were 

 covered with black paper, except on the side toward the light 

 where a small window, 3 cm. wide, and extending from near the 

 top to the bottom of the dish was cut. The dish was placed so 

 that its middle point was at a distance of 50 cm. from the lamp, 

 at which point the light had an intensity of about 192 candle- 

 meters. Between the lamp and the dish, and 15 cm. from the 

 former, a screen with an opening 3 cm. high, and 1.5 cm. wide, 

 through which the light passed, was set up. 



The larvae used varied somewhat in size, but at the beginning 

 of the experiments the tadpoles were about 12 mm., the Ambly- 

 stoma larvae about 18 mm. long, none of them being shorter than 

 15 mm. During the course of the experiments, which were be- 

 gun early in April, and continued through May and part of June, 

 the larvae grew in size, until the tadpoles were about 20 mm., 

 the Amblystoma 30 mm. long. 



In order to find out whether the larvae were sensitive to light 

 received through the skin, it was necessary to remove their 

 eyes. The method used for removing the optic vesicles was that 

 described by Lewis ('04, '05 and '07) and by LeCron ('07). 

 The instruments used were a pair of very finely ground Noyes 

 iridectomy scissors, and a fine pointed pair of forceps for hold- 

 ing the embryos. The stage at which the tadpoles were operated 

 is that figured by Harrison ('04, p. 201) when the tail bud is just 

 beginning to be perceptible (fig. 1). The Amblystoma embryos 

 were operated at the corresponding stage (fig. 2) . All the em- 

 bryos were operated under a binocular microscope. They were 

 placed in watch glasses in a 0.2 per cent normal salt solution, in 



