1 78 "Journal of Comparative Neurology and Psychology. 



14. Segments of a colony orient, in general, like normal colo- 

 nies, but they usually take a spiral course, the width of which 

 depends upon the form and size of the segment and the part of 

 the colony from which it was taken. 



15. The direction of motion in Volvox is regulated by the 

 relative light intensity on opposite sides of the colony, regardless 

 of the ray direction. 



16. Orientation is not the result of "trial and error" reactions 

 as in Stentor, Euglena and other forms. Volvox colonies make no 

 errors in this process. 



17. There is no evidence of motor reaction in a Volvox colony, 

 taken as a whole. Orientation is, however, brought about by 

 motor reactions in the individuals which constitute the colony. If 

 opposite sides of a colony are unequally illuminated, the individuals 

 in the colony continually pass from regions of higher to regions of 

 lower light intensity and vice versa, as the organism rotates. This 

 change in light intensity induces motor reactions in the individuals, 

 which result in orientation of the colony. The motor reaction 

 in positive specimens is induced only when the intensity to which 

 the zooids are exposed is decreased, and in negative colonies only 

 when it is increased. 



18. In general, Volvox is positive in comparatively low and 

 negative in comparatively high light intensities; that is, it has an 

 optimum, but the optimum varies in the extreme. Colonies were 

 found to be negative in intensities ranging from 57 to 5000 candle 

 meters. The threshold also varies greatly, the lowest found being 

 0.14 candle meters. 



19. Change in the sense of reaction can be induced by change 

 in light intensity. It depends upon the physiological condition 

 of the organism and the time of exposure as well as upon the inten- 

 sity of the light. It cannot be induced by mechanical stimulation 

 or change in temperature. 



20. When compelled to move practically perpendicular to the 

 rays, Volvox can still find its optimum in a field of light graded 

 in intensity. Under such conditions it collects in the optimum 

 intensity by merely wandering movements. There is no evidence 

 of orientation or "trial and error" reactions of the kind that were 

 found in Stentor under similar conditions (Mast '06, pp. 366-3 77). 



21. If jars containing Volvox colonies are exposed to light 

 from a single source, those specimens which contain large daughter- 



