38 IOWA STUDIES IN NATURAL HISTORY 
are now distinguishable with certainty. But where is the 
material in abundance to work up other faunas? A certain 
amount is available on this side of the water, but the inaccess- 
ibility of the European collections makes difficult hard-and-fast 
tenable determinations. Collections of aquatic Hemiptera here 
and abroad are entirely inadequate. These insects are not the 
favorites of collectors; they are picked up in the most casual 
manner here and there; and later inadequately characterized 
by perfectly competent entomologists with an entirely super- 
ficial knowledge of the aquatic groups of Hemiptera as a whole 
—a knowledge very necessary to a proper discrimination and 
appreciation of characters, as well as to adequate descriptions 
based on fixed structures. 
But nothing will ever be done permanently on any of the 
groups of aquatic Hemiptera until they are put on a thorough- 
going basis of pure structure. Anything other than this is 
trifling and negligible. 
