148 Dr. C. A. Kofoid on Pleodorina illinoiseni?is. 



In tlie majority of instances where tlie direction of rotation 

 was observed it was from right over to left, the ratios being 

 22 to 16, and 35 to 30. Tiiese tables give some idea of the 

 frequency of change in direction ;ind its variation in different 

 individuals, but do not show the duration of the directions of 

 rotations. Tin's is indicated in a general way in the second 

 table by the plus and minus signs, whicli sliow the direction 

 in which the rotation was of longer and shorter duration. 

 In conclusion it may be said that both directions of rotation 

 occur, though that from right over to left is more frequently 

 met with, or, in other words, is of longer duration. 



With regard to locomotion in P. calif ornica, Shaw (1894-) 

 says that " the movement of the plant in the water was fol- 

 lowed in the case of a ie^^ individuals bearing well-developed 

 gonidia. In swimming through the water the vegetative pole 

 is directed forward and the plant revolves to the right (in 

 observed cases) on the axis connecting the vegetative and 

 reproductive poles. The path is parallel to this axis in up- 

 ward vertical as well as in horizontal movement." The 

 polarity of this genus thus expressed physiologically in the 

 movements of the colony is accompanied by a corresponding 

 structural differentiation of the cells composing the organism. 



In Oonium, according to Fresenius (1856), the motion of 

 the colony resembles that of a wheel, progression taking place 

 in the line of the axis of rotation. According to BUtschli 

 (1883-1887, p. 858), locomotion is accomplished by the 

 rotation of the plate-like colony around its shorter axis, the 

 direction of rotation being to the right in some individuals 

 and to the left in others. Pfeffer (188 J:), on the other hand, 

 describes the rotation during the forward movement as alter- 

 nately from the right and the left. Migula (1890) calls 

 attention to the wavering, often backward, and irregular 

 movements of this genus, and also notes its rotation about 

 an axis through the middle of the colony. This rotation is 

 either to the right or to the left, no predominance being men- 

 tioned. Polarity is thus marked in the activity of the Gonium 

 colony, though not expressly marked in its structure except 

 as it appertains to the individual cells. 



