LIGHT REACTIONS AND PHOTOTAXIS 607 



Unlike the Californian form used by Loeb my nauplii showed 

 no lack of precision in their response to changes of concentration. 



To sum up, we may repeat the names of all the agents experi- 

 mented with, classed in three groups. The first contains those 

 with a positivating effect, including sodium, potassium, acids, 

 deoxygenated seawater, hypertonic seawater and decrease of 

 temperature. The second contains those with a negativating 

 effect, including certain visible and invisible light rays, alkali, 

 traces of metal, hyjDotonic solution and increase of temperature. 

 The third contains narcotics, causing the animals to lose their 

 sensitiveness to light and including calcium, alcohol, ether and 

 chloroform. 



I will conclude the account of my work on Balanus nauplii 

 by a number of experiments made to test the influence of vari- 

 ous dyes on phototaxis. The larvae were transferred for some 

 time into solutions of stains and then exposed to hght of differ- 

 ent wave lengths either in these solutions or in pure seawater. 

 I tried methylene blue, eosine, erythrosine, Bismarck brown, 

 methyl green, neutral red and orange. The effect of staining 

 on the hght reactions was ascertained by comparison with un- 

 stained animals, special care being taken to keep both stained 

 and unstained animals under equal conditions. The water was 

 always taken out of the same aquarium for both sets of animals. 

 The only variable was the addition of the dye. 



I soon observed that animals which had been stained in Bis- 

 marck brown or methylene blue became negative more quickly 

 than unstained larvae when exposed to white hght. It was 

 sufficient for the animals to remain for one or two hours in a 

 solution with just a shade of brown or blue color, to obtain this 

 result and the same effect was reached when the animals were 

 put into the color solution and exposed to light at once. With 

 eosine the effect was very slight and not always observable and 

 with the rest of the dyes no effect was seen at all. 



I then exposed animals stained brown or blue to strong arti- 

 ficial hght made monochromatic by color solutions. I used a 

 solution of potassium monochromate for the yellow and a solu- 



