l6o Frank W. Bancroft 



can easily be followed under the compound microscope, without 

 the addition of any sticky substances to the culture fluid. 



If now a current be passed through such a preparation of volvox 

 that has been exposed to weak light, strongly anodal colonies can be 

 picked out and investigated. In such colonies it was invariably 

 and frequently observed that the currents stopped or became very 

 weak on the anode side of the colony while it was not changed 

 much at the cathode side. Sometimes there was no change at 

 the cathode side, and sometimes there was a decided increase in 

 the activity of the flagella when the current was made, and during 



^^ 



Fig. 2 Diagram of volvox, showing the direction of the currents in the surrounding medium when 

 the colony is swimming in a constant current, i, anode on the side. The currents stop on that side 

 and the colony turns toward the anode. 2, anode at anterior end. There are no currents at the anterior 

 end, and the colony swims toward the anode. 3, the current has just been reversed, so that the anterior 

 end is now cathodal. Currents have started at the anterior end, and have stopped at the posterior (now 

 anodal) end. 



the flow of the current. The same change in the behavior of the 

 flagella was observed at the two poles no matter what the position 

 of the organism. If it is swimming at right angles to the current 

 lines then the flagella on the anode side stop, while those on the 

 cathode continue and the organism is rapidly turned toward the 

 anode (Fig. 2), and continues swimming in that direction. When 



