294 STUDIES IN GENEEAL PHYSIOLOGY 



Another condition must, however, be taken into con- 

 sideration, which may have the effect that animals which 

 are constantly positively heliotropic must leave the surface 

 of the water at higher temperatures. As is well known, the 

 processes of oxidation, and consequently the demand for 

 oxygen, rise considerably with an increase in temperature. 

 It is natural that when the demand for oxygen exceeds the 

 supply, the animal can execute no, or only weak, swimming 

 motions, and in consequence falls to the bottom. At any 

 rate, the latter can, indeed, be observed at high tempera- 

 tures. Loligo larvae which hold themselves at the surface 

 by swimming motions sink passively as soon as the tempera- 

 ture exceeds 30 C. 



In conclusion I wish to add that I made experiments on 

 most of the animals mentioned in this paper with colored 

 light, and found a universal confirmation of the fact, which 

 I discovered before, that the more strongly refrangible rays 

 of the visible spectrum are the most active heliotropically, 

 as in the case of plants, 



