350 H. C. VAN DER HEYDE 



two factors. In each experiment the time spent at the surface 

 was determined by means of a stop-watch and tabulated. The 

 experiments lasted half an hour; in the table I also indicated 

 the ten-minute periods. 

 The experiments wxre: 



TABLE 3 

 Experiment 1. Dytiscus d'. Water normal. 

 7.3; 10 min. ; 35; 20 min. ; 1.2. Total 48. 

 Experiment 2. Dytiscus cf . Water boiled. 



5.2.32.150.7.5.15.7.47; 10 min.; 7.5.3.3.7.7.105.6.5.13; 20 min.; 1.1.1.1.18.9.1. 

 160.10.63. Total 270 + 162 + 264 = 696. 

 Experiment 3. Dytiscus c?'. Water normal. CO2 atmosphere. 



In the first 10 min. the animal stayed about 100 sec. under water, after that 

 it was about continuously at the surface. 

 Experiment 4. Dytiscus (d. Water normal. H2 atmosphere. 



20.2.1.2.60.5.34.40.55.50.3.25; 10 min.; 50.4.1.15.150.230.5.10.120.5.10.120; 20 



min.; 70.30.145.31.65.80.150. Total 297 + 585 + 570 = 1452. 

 The animal gave the impression that it M'as not able to dive. Perhaps the 

 hydrogen gives a marked decrease in specific gravity so that it is made 

 very difficult for it to dive. 

 Experiment 5. Dytiscus cf. Water boiled, allowed to cool and then saturated 

 with carbon dioxide. Air normal. 



2.2.6.2.5.1.1.16.1.2.1.1.1.4.7; 5 min.; 5.1.29.1.1.2.1.1.1.4.1.12; 10 min.; 2.71.4. 

 1.60; 15 min.; 55.1.3; 20 min.; 2.28.32; 25 min.; 14.3.5.4.2.4.21.4. Total 

 111 + 197 + 119 = 427. 



These experiments show clearly that not only the composition 

 of the atmosphere, but also the gas content of the water has a 

 noticeable influence on the animal's behavior, as far as breathing 

 is concerned. When we compare, for instance, experiments 1 

 and 2, we see a remarkable increase in the number of times in 

 which the animal goes to the surface and in the time spent there. 

 This is only due to the fact that in one case the gases have been 

 expelled from the water so that the air in the air-store must dif- 

 fuse out. Very remarkable in this connection is the fact that 

 less time is spent at the surface when the water after having been 

 boiled and allowed to cool is saturated with CO2 (exp. 5). In 

 that way CO2 cannot diffuse out and decrease in volume is at a 

 much slower rate. 



In the second place, these experiments show once more that the 

 importance of this gas diffusion has not been realized sufficiently 



