PHYSIOLOGICAL EFFects oF Lack oF Oxycen 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. JI 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hours when oxygen is withdrawn.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 
Digitized by Microsoft® 
