b S. O. MAST 



4. PROCESS OF ORIEM ATION IN GONIUM 



The observations on orientation in Gonium were made in es- 

 sentially the same way as those described in earlier works (Mast 

 '11, pp. 92-96) it will consequently not be necessary to discuss 

 methods here. Ihe results of these observations follow: 



Gonium swims in a fairly direct course with the flat surface 

 perpendicular to the direction of motion. The surface with the 



o.o3 mm 



Fig. 4 Camera lucida sketch of a longitudinal section of Eudorina nearly 

 through the middle showing two of the four anterior zooids. No. 6 comp. ocular; 

 1^2 homo, oil immersion objective, a, anterior end of colony; s, outer surface; n, 

 nucleus; p, pyrinoid; e, eye-spot; mm, projected scale. The eye-spot in this form 

 is essentially like that in Gonium but it is much larger and the two parts can be 

 much more distinctly seen. The best lenses available fail, however, to reveal 

 any differentiation in these two parts in either form. Drawn by Caswell Grave. 



flagella is always ahead. As it proceeds it continuously rotates, 

 usually counter-clock-wise as seen from the rear, although it 

 reverses frequently and rotates in the opposite direction for short 

 periods of time. It orients fairly accurately in light, being ordi- 

 narily positive in moderate and negative in strong illumination. 



