390 CHRISTINE ESSENBERG 



the surface when at rest. This, however, may be due to the 

 fact that in an aquarium without any weeds or sticks the sur- 

 face film serves as the only medium of attachment. A stronger 

 evidence in favor of negative geotropism is that the bugs, when 

 placed on the wall, always crawl upward. Again, when the bugs 

 are placed in a high jar which is kept in diffused light or in 

 perfect darkness, they always rise to the top as soon as the jar 

 is reversed. But here we have to deal with two factors, the 

 need of oxygen in the closed jar, and the negative geotaxis. 



Notonectas are positively rheotactic, always swimming against 

 the current. They have positive thigmotaxis and usually are 

 attached to some object when at rest. Sometimes they are 

 attached to one another, three or four in number. 



SUMMARY 



Notonectas are widely distributed. They are very voracious 

 and attack animals many times their own size. The insects 

 are well protected by the thick layer of surrounding air, hence 

 chemicals have very little influence on them. Notonectas have 

 a strong positive phototaxis. The phototaxis increases with the 

 increase of the temperature and with greater light intensity. 

 When exposed to arc light or to bright sunlight, they imme- 

 idately take to their wings, flying toward the light. At a tem- 

 perature of zero centigrade they become chilled, lose their air, 

 and drop to the bottom of the aquarium and die if the aquarium 

 is deep. They are positively rheotactic, always swimming against 

 the current. The young hatch within twenty days and are well 

 adapted to their environment from their very first day of life. 

 They resemble the adults in their behavior and instincts. 



LITERATURE CITED 



Kirkaldy, G. W. Miscellaneous Rhynchotalia. The Entomologist, 34, 5-6. 



1897. Revision of the Notonectidae. Trans. Entom. Soc, London, 4, 392-426. 

 Buena, J. R. de la Torre. The Genus Notonecta in America, North of Mexico. 



1905. Journ. N. Y. Entom. Soc, 13, 143-167. 



1908. Concerning the Notonectidae and Some Recent Writers on Hemipter- 

 ology. Canad. Entom., 40, 210-211. 

 Delcourt, A. De l'influence de la temperature sur le development de Notonecta. 



1908. C. R. Ass. France Av. Sc. Sess., 36, 244-245. 

 Holmes, S. J. Phototaxis in Ranatra. Journ. Cotnp. Neur. and Psvch., 15, 305. 



1904. 

 Hoppe, Julian. Die Atmung von Notonecta glauca. Zool. Jahrb. Allg. Zool. 



1912. & Physiol, 31, 189-224. 

 Severin, Henry H. P., and Harry C. Severin. Notonecta undulata Say preying 



1910. on the eggs of Belostoma (Zaitha auct.) flumineum Say. Canad. 

 Entom., 42, 340. 



