MOTOR RESPONSES 329 



in this environment must be due to changes in the colony itself. Since 

 photopositive response is specifically correlated with cathopositive re- 

 sponse, and photonegative response with anopositive response, the differ- 

 ence in the response to electricity must be due to like changes in the 

 colony. The only difference observed in the colonies in connection with 

 the response to light concerns the electric charge. Referring to this, Mast 

 (1927c) says: 



Most of the photopositive colonies observed drifted toward the anode 

 and most of the photonegative ones drifted toward the cathode, indicating 

 that the former were negatively and the latter positively charged. However, 

 owing to the negatively charged glass bottom of the aquarium in which 

 the observations were made, there was produced in the solution near the 

 bottom an endosmotic current of water toward the cathode and this current 

 produced at the upper surface a current in the opposite direction, i.e., toward 

 the anode. In making the observations it was impossible to ascertain pre- 

 cisely the location of the colonies in relation to these currents, resulting fre- 

 quently in uncertainty as to whether the drift was due to cataphoresis or 

 to endosmosis. The results obtained are consequently somewhat equivocal. 



These observation should therefore be repeated under more favorable 

 conditions, for the results are of fundamental importance in the analysis 

 of the mechanics of the response to electricity, as will be shown pres- 

 ently. 



Mechanics of response. — The outstanding characteristics of the re- 

 sponses to the electric current of the colonial forms, exemplified in 

 Volvox, consist in momentary decrease in the action of the flagella, cor- 

 related with the direction and the density of the current and the nature 

 of the response to light. In photopositive colonies this occurs in such a 

 way that the flagellar activity decreases on the cathodal side after the 

 current is made. In photonegative colonies the activity decreases on the 

 anodal side, continues a few seconds, and then increases again. But if 

 the current is broken, it decreases on the opposite side, continues a few 

 seconds, then begins again. The extent of the region affected under all 

 conditions varies directly with the density of the current. 



The action of the current must be due to movement of ions, parti- 

 cles, or fluid in the colonies or the surrounding solution, and to differ- 

 ences in the responses in photonegative and photopositive colonies to 

 differences in the effects produced by the movements of these substances. 



