PHYSIOLOGICAL EFFECTS OF LACK OF OXYGEN 419 



were also found at the window side of the vessel. A second 

 small collection occurred in the middle of the vessel, while 

 the room side of the vessel was entirely vacated. The ani- 

 mals usually did not become positively heliotropic until 

 shortly before they became motionless. This explains why 

 the conversion of the negatively heliotropic into the posi- 

 tively heliotropic animals through lack of oxygen cannot be 

 obtained with the precision and elegance with which the 

 change can be obtained by cooling. In the latter case the 

 animals retain their full power of movement; in the former 

 the transformation does not occur until the animals have 

 suffered from lack of oxygen. But even then the phenome- 

 non is so striking that it might be used as a demonstration 

 experiment. I have repeated the experiment eight times 

 with the same result. At first it seemed to me as if the 

 negatively heliotropic Copepods died more rapidly in the 

 absence of oxygen than those which were positively helio- 

 tropic from the beginning. This finding, however, was not 

 borne out in every case. 



When the experiment was interrupted early, at a time 

 when the animals first began to become positively heliotropic, 

 and air was then admitted, the Copepods which had become 

 positively heliotropic again became negatively heliotropic. 



The remarkable effects, which we have described here, of 

 lack of oxygen on the sense of heliotropism, are, of course, 

 not confined to Copepods. I made similar experiments upon 

 the negatively heliotropic marine Isopods, the majority of 

 which also become positively heliotropic in less than two 

 hours when oxygen is withdrawn. These experiments will 

 be continued. 



We see, therefore, that lack of oxygen has the same 

 effect upon the sense of heliotropism as cooling or increas- 

 ing the concentration of the sea-water. Araki has shown 

 that by cooling the chemical effects of lack of oxygen can 



