282 LIGHT AND THE BEHAVIOR OF ORGANISMS 



the bottom and become slightly negative to light. On 

 August 6, 1909, a considerable number of larvae, a few 

 hours after they had emerged from the egg-strings, were 

 put into each of several small glass aquaria containing sea 

 water. The larvae were strongly positive in the light 

 ' intensity in which they were exposed. To one of the 

 aquaria distilled water was added drop by drop, until the 

 larvae no longer responded to light ; to another concentrated 

 sea water was added, and to each of the others a weak 

 solution of one of the following chemical compounds: 

 chloroform, adrenalin, atropin, carbonic acid, hydro- 

 chloric acid, acetic acid, magnesium sulfate, magnesium 

 chlorid, ammonia and sodium hydrate. 



After the larvae became neutral in each solution, they 

 were left undisturbed. If they became positive in the 

 course of a few minutes, as frequently happened, the solu- 

 tion was made stronger until they became neutral again. 

 In the solutions containing carbon dioxid, caffeine, dis- 

 tilled water or concentrated sea water, the larvae became 

 negative in the course of a few minutes and collected at the 

 side of the aquaria farthest from the source of light, but in 

 no instance was the negative reaction as marked and 

 precise as the positive had been. There was no very 

 definite orientation in the negative specimens, no such 

 streaming from the source of light as there is toward it 

 under normal conditions. Many of the larvae in each 

 solution settled to the bottom of the aquaria and remained 

 there, having apparently lost all power to respond to light. 

 The larvae in the solution containing magnesium sulfate, 

 magnesium chlorid, hydrochloric acid, acetic acid, ammonia, 

 sodmm hydrate or atropin, also became negative, but it 

 required a much longer time. In some of these solutions 

 the larvae did not become negative until several hours 

 after the compounds had been added. 



After becoming negative the larvae usually remain so 

 permanently, or at least for several hours. For example, 

 those which became negative in the afternoon of August 6 



