OBSERVATIONS ON UNICELLULAR FORMS 1 25 



direction when the larger end is ahead. Early in the fore- 

 noon after the jars have been in darkness all night the 

 spores usually all swim with the larger end ahead, but later 

 in the day they proceed with the other end foremost. I 

 was however unable to induce this change by keeping them 

 in darkness during the day. The following quotation from 

 my notebook serves to emphasize this peculiar reversal : 

 On the morning of January 10 all swam with the larger 

 nonciliated end forward rotating counter-clockwise as seen 

 from the posterior end. Most of them swam rather actively 

 in closed curves circling toward the left. In the afternoon 



I was surprised to find all the spores swimming about with 

 the smaller end, the end containing the cilia, ahead. They 

 were very abundant in the jar and quite active. The jar 

 was in strong light all day, part of the time in direct sun- 

 light, and although they were most numerous on the wall 

 of the jar facing the window, they gathered on the side 

 under the cover-glass farthest from thewindowwhen exposed 

 to the direct rays of the sun. On the morning of January 



II there were but very few motile specimens, but all that 

 were observed excepting one swam as those found on the 

 preceding morning did, i.e., with the larger end ahead. At 

 2.30 P.M. they were slightly more numerous and nearly all 

 swam with the smaller end ahead. I am, at present, un- 

 able to account for this reversal in locomotion. 



These organisms are so small, move so rapidly, and are so 

 nearly S3^mmetrical that it was impossible to ascertain under 

 normal conditions whether or not they always turn toward 

 the same side in their orienting reactions. They were 

 therefore mounted in a solution of quince-seed jelly. In 

 this solution they swim about very slowly; they stop fre- 

 quently, back some distance, turn toward one side and 

 then proceed on a new course; that is, they respond with 

 the avoiding reaction. If the solution contains consid- 

 erable jelly they frequently swim with the posterior end 

 ahead. 



By focusing attention upon specimens in which the 



