HELIOTEOP1C TRANSFORMATION 115 



negativation. In two minutes all the animals are col- 

 lected in a dense cluster on the negative side which lasts 

 for about 35 minutes. A weak negative collection could 

 also be obtained by adding 0.1 c.c. of a 0.5 per cent, solu- 

 tion of strychnine nitrate. Moore found that if the Diap- 

 tomus were first made positively phototropic by the addi- 

 tion of alcohol or acids, it was impossible to alter their 

 response by the action of caffein, strychnine, or atr opine. 

 On the other hand, animals which had formed a negative 

 collection under the influence of caff ein if treated with car- 

 bonated water at once changed their response and swim- 

 ming to the light side of the dish formed a positive 

 gathering. 



What causes these effects? The fact that alcohols 

 make the organisms positively heliotropic suggested the 

 possibility of a " narcotic " effect; the writer found, how- 

 ever, that narcosis requires a concentration of alcohols 

 three times as high as the one required to produce positive 

 heliotropism. He tried the effect of temperature on 

 the reversal of the sign of heliotropism in Daphnia and 

 found that lowering of the temperature enhanced the 

 effect of acids in making the animals positive. 296 



The writer had found previously that in marine crus- 

 taceans and in larvae of a marine annelid, Polygordius, the 

 sense of heliotropism can be reversed by changes of tem- 

 perature as well as by changes in the osmotic pressure 

 of the sea water. 291 Increase in the osmotic pressure of 

 sea water (by adding about 1 gm. of NaCl or its osmotic 

 equivalent of other substances to 100 c.c. of sea water) 

 made the negative animals positively heliotropic, and 

 lowering of the concentration by adding 30 to 60 c.c. dis- 

 tilled water to 100 c.c. sea water made positive organisms 

 negative. Negative larvae of Polygordius or negative 



