92 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. Hight 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 
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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. 
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