336 H. C. VAN DEE HEYDE 



The mechanism of their respiration was already known to 

 Swammerdam; he also knew that breathing in Dytiscus is entirely 

 different from that in Hydrophilus. The old naturalist Frisch^ 

 had not seen it, and in observing Dytiscus only was led to gener- 

 alize. Nitzsch,^ a more careful observer, corrected this and 

 emphasized the difference between the two species. 



It is not my intention to give a complete history of our knowl- 

 edge of this problem. Such review should be absolutely com- 

 plete or not be given at all. Moreover, the interested reader can 

 find a complete though not wholly impartial summary of the 

 older investigations (till about 1912) by Babak in Winterstein's 

 Handbuch der vergleichenden Physiologie, I. Bd., 2 Halfte, p. 452 

 seq., while most of the more recent studies have been mentioned 

 in Ege's paper. ^ 



The problem to be solved here has many sides. In the first 

 place, the animal must be able to stay for a certain time in the 

 water. In consequence of its type of organization, however, it 

 is not entirely independent of the atmospheric air. Intermit- 

 tently it must come to the surface to breathe, and now the problem 

 has to be solved how to penetrate the surface layer. This prob- 

 lem has been solved in an entirely different way by Dytiscus 

 and Hydrophilus. 



Dytiscus breathes with the edge of its abdomen. By com- 

 plicated movements of this abdomen which have been studied in 

 great detail by du Bois-Reymond^ and Plateau" and in which the 

 muscles of the ' Genitalkapsel ' play an important role — these 



2 J. L. Frisch. Beschreibung von allerley Insekten in Teutschland. 2 Teile. 

 Berlin, 1721. 



3 Ch. L. Nitzsch. Ueber das Athmen der Hydrophiliden. Arch. f. Phys. 

 Reilund Autenrieth., Bd. 10, S. 440, 1811. 



* Rich. Ege. On the respiratory function of the airstores carried by some 

 aquatic insects (Corixidae, Dytiscidae and Notonecta). Zeitschr. f. Allg. 

 Physiol., Bd. 17, S. 81, 1918. 



5 R. du Bois-Reymond. Ueber die Atmung von Dytiscus marginalis. Ver- 

 handl. der deutschen Physiol. Ges. Arch. f. Phys., 1898, S. 378. 



* F. Plateau. Recherches experimentales sur les mouvements respiratoires 

 des insectes. Bull. Acad. Roy. Belg., T. 3, p. 727, 1882. 



