THE MECHANISM OF ORIENTATION IN GONIUM 



A. R. MOORE 



From the Physiological Laboratory of Rutgers College, New Brunswick, N. J. 



TWO FIGURES 



Recently Mast^ has published a paper in which he tries to 

 account for the mechanism of orientation in Gonium, using light 

 as a directive stimulus. In 1911 Goodspeed and 1- published 

 an account of the orientation of the same form under the influ- 

 ence of a galvanic current. Mast does not seem to have been 

 acquainted with our article since he makes no reference to it, 

 although he confirms in the main, our observations. 



In neglecting to make a study of the stroke of the individual 

 flagellum. Mast has failed to consider an important factor and 

 perhaps the chief factor in the orientation mechanism of this 

 form. It seems necessary, therefore, to call attention to the 

 analysis of orientation in Gonium which Goodspeed and I pub- 

 lished five years ago. Since our paper appeared in a journal not 

 readily accessible, I quote the section dealing directly with the 

 subject in question. 



In moving through the water the Gonium colony, in general, keeps 

 its plane perpendicular to the line of direction. This may be modified 

 by a more or less 'wobbly' motion. In addition to the progressive 

 movement the colony rotates in its own plane. The direction of the 

 rotation reverses frequently, seemingly without reference to the amount 

 of linear motion. At times the rotation is suspended for a moment, 

 while the organisms are moving forward. 



With reference to the colony, the fiagella extend forward and out- 

 ward. In making a stroke occasionally the entire flagellum takes part, 

 but usually only the peripheral one-half or one-third is used, while the 

 inner part remains practically rigid. The stroke made by the active 

 part of the flagellum describes a cone, the effective component of which 

 is backward. There must be in addition a secondary effective com- 

 ponent of the flagellar stroke in order to bring about the rotary motion. 



If we observe the movement of an isolated cell it will be seen to 

 describe a circle with the anterior end, in addition to moving forward. 

 These two simultaneous movements cause the cell to follow a spiral 

 path. If the cell reverses the direction of its progress it turns about 

 in a wide half circle always keeping the flagella ahead. The turning 

 may be accomplished by the flagella in one of two ways: 1) One fla- 



1 Mast, S. O., Jour. Exp. Zool. vol. 20, p. 1. 



2 Moore, A. R., and Goodspeed, T. H., Univ. Call. Publ. Physiol, vol. 4, p. 17. 



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