344 



H. C. VAN DER HEYDE 



TABLE 2 



These figures show once more: 1) that the animal expires as 

 soon as it comes to the surface; 2) that the air-store at the end 

 of the period during which the animal remains in the water con- 

 tains much nitrogen, little oxygen, and less carbon dioxide than 

 one would expect. 



3. In insects, contrary to what we find in vertebrates, expira- 

 tion takes place actively as, according to Ege, Brocher^^ strongly 

 emphasizes. 



4. Dytiscus is able to obtain' some oxygen through diffusion 

 from the water. What this means and in how far this oxygen 

 intake has a biological importance will be discussed later on. 

 Here I simply describe the following experiment. 



One beetle was put into a beaker. In order to avoid as ranch 

 as possible the diffusion of oxygen from the air into the water, I 

 covered the surface with a floating cork with a little hole in the 

 center for breathing (paraffin oil cannot be used, as stated pre- 

 viously). Moreover, the beaker was covered by a glass plate. 



Before and after the experiment the oxygen content of the 

 water was determined by the method of Winkler, ^^ 



Experiment A. Animal in the water during 2| hours. Before 

 the experiment: 11.27 cc. thiosulphate. After the experiment: 

 10.47 cc. Difference: 1.80 cc. 



1^ His paper, Recherches sur la respiration des insectes aquatiques adultes. 

 II. Les Dytiscides. Ann. de Biol. Lacustre, T 4, 1909/11, was not available for 

 me. 



15 1 did not yet know the remarkable improvement of this method by Edwin B. 

 Powers, published in the Bull. o. the 111. State Lab. o. Nat. Hist., vol. 11, May,. 

 1918. 



