Nos. 622-623] ORGANIC EVOLUTION 



533 



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 6 (Table I). Thus 



TABLE I 



A series of aquatic microorganisms showing in general the clockwise rotation 

 of positively phototactic forms ami the counter-clockwise rotation of nega- 

 tively phototactic forms in the northern hemisphere, with evidence for the 

 tendency to reverse condition in the southern hemisphere. 



Eiif/lcna npirogyra Ehr. 



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

 positively phototactic forms with the exception of 



fact tha^a'sV^ imperfectly known, reverse 



movements may occur, e. g., the negative response of Euglenoids to intense 

 light. 



