352 H. C. VAN DER HEYDE 



SUMMARY 



With a new apparatus the mechanism of breathing of Dytiscus 

 marginahs L. is studied. The movements of a droplet of petro- 

 leum are observed when the animal is allowed to breathe in a 

 space which is closed by this droplet. It appears that the first 

 observable movement is an expiration, which fact is in contra- 

 diction with previous statements of other authors. A theory 

 is given to explain this fact and in several ways the verification 

 of this theory is tried. With a new apparatus the air is studied 

 after the animal is allowed to breathe in it for some time. The 

 fact reported by Ege and Kreuger that the O2 in the air-store is 

 consumed during the animal's stay under water was proved 

 again. The biological importance of the oxygen diffusion into 

 the air-store is discussed from the physico-chemical standpoint 

 and treated mathematically. 



Finally, the relative importance of the gases in the water and 

 in the air for the animal's behavior is studied. It appears that 

 though the animal has become emancipated to a certain extent 

 from its original environment, it is still more dependent on the 

 air than on the gas content of the water. 



Thanks are due to Prof. Dr. Withrow Morse who tried to make 

 my English readable even for the English reader^ — and I trust he 

 succeeded- — and corrected the many mistakes. 



MoRGANTOWN, W. Va., U. S. A., January 6, 1921 



