432 A. R. MOORE 



gellum remains inactive while the other continues the normal beat 

 (fig. 1); 2) both flagella produce the effective component on the same 

 side (fig. 2). Nothing of the nature of a motor reflex was observed. 



Now Mast accounts for orientation to a directive stimulus by 

 supposing the zooids farthest from the source of light to increase 

 their activity and thus to bring the plane of the colony perpen- 

 dicular to the lines of the stimulating force. He assumes equal 

 activity of the two flagella in each cell of the colony, the behavior 

 of the cells varying only in the intensity of their activity. He 

 does not consider the possibility which Goodspeed and I pointed 

 out, viz. : that the turning may be accomplished by an inequality 

 in the beating of the two flagella of each cell. This we showed 

 to take place in the isolated cells of Gonium. In case 1 the 

 flagellum on the kathodal side ceases beating. This type of 

 orientation was observed by Bancroft' in Volvox. In case 2 

 the flagellum on the kathodal side reverses the direction of its 

 effective stroke. This mode of response was observed by Lud- 

 loff^ in Paramecia. 



The orientation of Gonium may therefore be accomplished 

 either by increased activity of the cells away from the side 

 stimulated, as Mast assumes, or by cessation of beat or reversal 

 of stroke of the flagellum on the stimulated side of each cell. 

 There remains the possibility that both types of reaction may 

 play a part in orientation. 



In view of the facts presented, it is clear that any thorough 

 analysis of the phenomenon of orientation in Gonium must in- 

 clude not only a consideration of the changes in the activity of 

 the cell as a whole but also of the differences in the activity of 

 the individual flagella of each cell. 



-h 



Fig. 1 Fig. 2 



3 Bancroft, F. W., Jour. Exp. Zool., vol. 4, p. 157. 

 ^ Ludloff, Archiv f. Ges. Physiol., vol. 59, p. 525. 



