254 HUBERT B. GOODRICH. 



seemed always to exist a definite relation between the position of 

 the fan and the direction of motion. The fans were the only 

 portion of the cells in contact with the solid support and there 

 seemed to exist no mechanism for locomotion in a fluid medium 

 without support. Other types of fan cells, as described below, 

 illustrate these points even more clearly than the "Canoe" cells. 

 The rate of motion of the "Canoe" cells was studied by plotting 

 their course with a camera lucida. Fig. 4 shows the history of such 

 a cell. In most cases the outline of the fan could not be observed 

 with the camera in position and an outline of only the body was 

 drawn. However, in positions I, 12, 21, 28, 30, 32 and 34 the 

 probable form of the fan is indicated by dotted lines. These 

 outlines were based on observations with the prism of the camera 

 removed. At position 8 the cell became attached by a psuedo- 

 podium-like projection on the right which may have terminated 

 in a fan. A similar process occurred at positions 24 to 35 during 

 which period a small fan could clearly be observed at the right. 

 At position 27 the cell under observation collided with another 

 cell. The two cells became attached and the newcomer formed 

 an irregular projection at the upper right of the original cell 

 (positions 27 to 36). 



The average rate of motion of freely moving cells excluding 

 such cells as proved to be slowing down prior to the death of the 

 cell, was 6.3 microns per minute. The cell shown in Fig. 4 moved 

 at a rate of 5.3 microns from positions I to 25. An attempt was 

 made to study the effects of changes of temperature upon the 

 movement of these cells. For this purpose the cultures were 

 studied under the microscope in a warmed box at temperatures 

 varying from 21 centigrade to 42. Above 40 the cells withdrew 

 their fans and became rounded. Observations were made at 

 constant temperatures and also during an increase of tempera- 

 ture. It soon became apparent that variations in the conditions 

 of individual cells would preclude the possibility of constructing 

 a temperature curve for the rate of locomotion. Cells becoming 

 free from the main growth of tissue moved for a variable period 

 and then became rounded and this condition probably pivceeded 

 the death of the cell. A slowing of the rate of motion was appare- 

 ent before the contraction took place. Also the varying torm of 

 the cell and the probable occasional attachment !>v small sub- 



