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STUDIES IN GENERAL PHYSIOLOGY 



Spirographis Spallanzanii, each about 15 cm. long, on the 

 bottom of the aquarium, with the longitudinal axes of their 

 tubes perpendicular to the plane of the window. Eight of 

 them lay with their oral poles toward the room side efgh 

 (Fig. 7) of the aquarium; one with its oral pole toward the 

 window side. The first two days passed without any change 



FIG. 7 



in the orientation; the animals first attached the aboral ends 

 of their tubes to the floor of the aquarium. In the course of 

 the third day the tubes of six of the animals, which were 

 placed with their oral pole toward the room side, began to 

 bend in an almost horizontal plane, the concavity of the curv- 

 ature being directed toward the window. The other two 

 animals, which had likewise been placed with their heads 

 toward the room side, first elevated the head end and then 

 curved the tube concavely toward the window. Finally, the 

 ninth animal, which I had placed in the aquarium with its 

 head toward the window, raised its head a little. 



