236 MARY O. McGINNIS 



APRIL 20, 1910. MALE APRIL 20, 1910. MALE 



Isttrial rUp,180sec. \^^ ^^.^^ fTo left, 30 sec. 



l^down, 10 sec. (to right, 40 sec. 



2nd trial (UP' ^0 sec. ^nd trial (^o left- 20 sec. 



(down 8 sec. (to right, 20 sec. 



3rd trial t^P' ^^ ^^^^ 3rd trial /^o left, 30 sec. 



(down, 22 sec. (to right, 20 sec. 



4thtrial fUp,80sec. \^^ ^^.^^ (To left, 20 sec. 



(down, 15 sec. (to right, 20 sec. 



5th trial (Up- 65 sec. ^^^ ^^.,^^ (To left, 13 sec. 



(down, 25 sec. , (to right, 12 sec. 



6th trial (Up. 15 sec. q^^ ^^.^^ fTo left, 30 sec. 



(down, 12 sec. (to right, 20 sec. 



Average /UP- 85.8 sec. ^^^^^^^ |To left, 23.8 sec. 



(down, 15.3 sec. (to right, 22 sec. 



An examination of these records reveals that Branchipus travels 

 downward in response to light more rapidly than upward, while 

 its rate of movement horizontally is about the same toward the 

 left as toward the right. The influence of gravity on the rapidity 

 of its locomotion in vertical planes is evident. 



It is to be noted that distilled water was used in all the experi- 

 ments concerned with gravity. This eliminated the possibility 

 of chemotropic reactions to foreign materials at the bottom of the 

 containers. Such reactions may be suspected to occur in an ordi- 

 nary aquarium in which deposits of debris are present. 



While the observations recorded above seem to warrant us in 

 holding that Branchipus is positively geotropic when exposed to 

 light, the methods used in obtaining the reactions do not enable 

 us to decide whether we are dealing with a definite orientation 

 with respect to the center of the earth, or with the purely mechani- 

 cal effect of gravity. It may be that the readiness with which the 

 animals seek the bottom is to be explained by their tendency 

 to sink in water. 



Reaction to gravity in darkness 



During the progress of the foregoing experiments it was noticed 

 that when specimens were left in the dark box with the curtain 



