336 A. C. WALTON 



Apparently no work has been done on the activating effect 

 of such light stimuli on the ciliary apparatus of Paramoecium, 

 though much has been done on the directive and orienting effect 

 of such stimuli. If different light intensities do cause an in- 

 crease or decrease in the ciliary motion of Paramoecium, it 

 might be exhibited in either of two ways, or by a combination 

 of the two: — (1) by causing increased or decreased rapidity in 

 the beating of the cilia, driving the animal along its normal 

 spiral pathway at different rates of speed; (2) by widening or 

 narrowing the curve of the spiral and hence decreasing or in- 

 creasing the forward advance of the animal while the rate of 

 motion is unchanged; or (3) by a combination of a change in 

 the rapidity of the ciliary action and a change in the diameter 

 of ihe spiral pathway. With the view of testing out these 

 possibilities, the following investigations were undertaken under 

 the direction of Dr. G. H. Parker, to whom the writer wishes 

 to express his thanks and appreciation for the careful super- 

 vision of the results embodied in this article. 



The animals used were all Paramoecium caudatum, obtained 

 from sixteen different cultures, and kept under varying condi- 

 tions of light. Individuals from three cultures that contained 

 conjugating lines were used at the same time as those from 

 non-conjugating lines, and careful records were kept to see if 

 the physiological factor was in operation. Some cultures were 

 kept in darkness for twelve hours preceding the trials, while 

 other cultures were exposed to day light or electric light for the 

 same period. The animals were placed in a hanging drop of 

 water one-half inch in diameter and so arranged on the stage 

 of the microscope that all light rays except those coming through 

 the condenser were entirely excluded. The observations were 

 conducted at a magnification of 25 diameters and camera trac- 

 ings were carefully made of the paths of the animals during 

 their exposure to the stimulus. The observations were all for 

 a period of one-half minute and the traced paths were carefully 

 measured with a planimeter. The stimulus consisted of a 32 

 c.p. Mazda bulb mounted on a sliding base and the intensities 

 of the stimulus varied from 5 to 1422 candle-meters, gained by 

 moving the light through the space between a point 15 cm. 

 and another 250 cm. from the microscope. A cooling stage, 

 through which cool distilled water was run, was used to prevent 



