146 THE SHORTER SCIENTIFIC PAPERS 



phototactic under normal conditions, it would immedi- 

 ately occur to one seriously considering the question, that 

 the underlying principle producing the rotation was the 

 turning of the earth on its axis, with the resultant appar- 

 ent motion of the sun from east to west. Such a hy- 

 pothesis would become the more tenable when it was 

 found that negatively phototactic microorganisms of the 

 northern hemisphere rotated as a rule in a reverse or 

 counter-clockwise direction. 



Some of the evidence thus far obtained may be pre- 

 sented more clearly in tabular form^ (Table I). Thus 



TABLE I 



A series of aquatic microorganisms showing in general the clockwise 

 rotation of positively phototactic forms and the counter-clockwise 

 rotation of negatively phototactic forms in the northern hemisphere, 

 with evidence for the tendency to reverse condition in the southern 

 hemisphere. 



Northern Hemisphere 



Euglena viridis Ehr. Positive. Clockwise. 



Euglena hcemogramdata Walt. Positive. Clockwise. 



Eugleita tripteris Duj. Positive. Clockwise. 



Euglena spirogyra Ehr. Positive. Clockwise. 



Leptacinclis ovtim (Ehr.) Positive. Clockwise. 



Phacus pyrnm (Ehr.) Positive. Clockwise. 



Cryptomonas ovata Ehr. Positive. Clockwise. 



Vandorina morum (Miill.) Positive. Clockwise. 



Eiidorina elegans (Ehr.) Positive. Clockwise. 



Volvox globator (Linn.) Positive. Clockwise. 



Stentor polymorpbtis Ehr. (=v/r/</w).— Positive. Counterclockwise. 



Pbactis longicauda Ehr. Positive. Counterclockwise. 



Stentor cceruhis Ehr. Negative. Counterclockwise. 



Amirea cochlearis Gosse Negative. Counterclockwise. 



Arenicola cristata (larva) Negative. Counterclockwise. 



Chilomonas paramcecium Ehr.^ Negative. Counterclockwise. 



Southern Hemisphere 



Leptocinclis piriformis Cun. Positive? Counterclockwise. 



Phacus bacilli fer Cun. Positive? Counterclockwise. 



Leptocinclis mammilata Cun. Positive? Clockwise. 



it may be stated that so far as the facts are available, 

 positively phototactic forms with the exception of 



The rotation direction and light responses noted are those taking place under 

 normal conditions. The conclusions presented are not altered by the fact that as a 

 result of stimuli under conditions imperfectly known, reverse movements may occur, 

 e. g., the negative response of Euglenoids to intense light. 



