292 STUDIES IN GENERAL PHYSIOLOGY 



with a cap impermeable to light, the animals which are very 

 energetically positively heliotropic should not go under the 

 dark cap. The latter does, however, actually occur. Hence 

 another and more powerful circumstance is at work besides 

 the positive heliotropism, and this might be negative geot- 

 . ropism. The temperature in the 

 tube was everywhere the same in 

 these experiments. The need for 

 oxygen does not compel the animals 

 to come to the top in these experi- 

 ments, for when the eudiometer tube 

 is filled entirely with water, and the 

 FIG. 68 open end is turned downward into 



a larger vessel filled with water, the animals nevertheless move 

 from this vessel to the cap of the eudiometer, and remain here 

 even though fresh oxygen can reach the animals at this point 

 only through diffusion from below. The significance of this 

 negative geotropism (which I believe it to be) for the upward 

 movement of the Loligo larvae is shown still more beautifully 

 in the following experiment : AB (Fig. 68) represents a 

 vertical section through the plane of the window; CD is 

 a eudiometer tube filled with sea-water and closed with a 

 cork. If the larvse at the beginning of the experiment are 

 collected at the room side C of the tube, they all move to 

 the window side D in consequence of their positive heliot- 

 ropism, and remain there. If, on the other hand, the tube 

 is so placed that it is at an angle with the horizontal for 

 example, in the position Cf> the Iarva3 gradually but 

 steadily rise by active swimming movements away from the 

 window to the elevated end C l and remain there. They 

 therefore leave the window side and go to the room side, in 

 spite of their positive heliotropism. To accomplish this the 

 angle Cf>C must in this case be not smaller than about 20 . 1 



1 The papers of Wolfgang Ostwald seem, however, to indicate the possibility of 

 a purely physical explanation of this experiment. [1903] 



