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THE AMERICAN NATURALIST [Vol. LV 



tions, notably those of Von Siebold ('58), W. Miiller 

 ('89), Marchal ('00), Eousseau ('08), Heymons ('08;, 

 Schulz ('07, '10% 'lO''), and Matheson and Crosby ('12), 

 have added much of interest, not only in bringing to light 

 aquatic members of several families, but in determining 

 some of the host species upon which they prey. In many 

 cases the adaptation to aquatic life is not so perfect as 

 the cases just mentioned, although several other species 

 are known to swim readily, using either the legs or wings, 

 which usually show modifications adapted to such be- 

 havior. 



In view of the frequent occurrence of aquatic imaginal 

 forms in other orders of insects such as the Coleoptera 

 and Hemiptera, it is perhaps not surprising to find cer- 

 tain parasitic Hymenoptera adopting this habitat. 

 Viewed more in detail, however, the matter is quite a 

 different phenomenon. Such Coleoptera as Gyrinidae, 

 Hydrophilidae, Dytiscidae, etc., are uniformly aquatic in 

 both preparatory and imaginal stages, and such is also 

 true of the brachycerous Hemiptera. All of these insects 

 are highly modified to conform with their aquatic envi- 

 ronment, particularly in reference to the functions of 

 locomotion and respiration. 



In the aquatic Hymenoptera, a series of families is 

 represented and only a comparatively small number of 

 genera are included. The structural modifications are 

 far less profound, indeed they frequently represent very 

 slight changes. They are more closely parallel to the 

 natatorial habit shown in isolated genera such as the rice 

 water-weevil, Lissorhoptus simplex, a beetle that has be- 

 come aquatic and oviposits in the roots of the rice plant 

 (Tucker, '12). It has been showTi experimentally by 

 Szymanski ('18) that many terrestrial insects may be 

 induced to swim if submerged and we may easily suppose 

 that the truly aquatic hal)it of the parasitic Hymenoptera 

 just mentioned ni.ix arisen through the seeking of 



their hosts in n<jualic iiiants, iirst at or above the surface 

 of the water, and later through a search for further indi- 



