Form and Function. 



Of all the ecological groups of animals none shows more 

 splendid and ofttimes obvious adaptations of form to function 

 than do those that live in the water. Surrounded by a re- 

 markably uniform element, it is interesting to note how ani- 

 mals of the most diverse classification have been molded to a 

 common plan in response to the physical properties of the 

 medium in which they dwell. 



Not only have widely different organisms responded in a 

 similar manner to a common environment, but the very con- 

 stant and uniform conditions of our fresh waters throughout 

 the world have resulted in the greatest similarity of forms, 

 widely dispersed over the earth. 



The insect life of the water ^ords an especially interesting 

 study since it represents a secondary adaptation. It is believed 

 that insects were all terrestrial in the beginning, but that some 

 have invaded the waters and acquired those structural pecul- 

 iarities that enable them to cope successfully with conditions 

 in a medium some 775 times as heavy as air. 



An examination of the insect fauna of the water will indicate 

 that it is a heterogeneous group, gathered together from the 

 various orders of insects, and illustrating different stages of 

 adaptation. 



As Bastin has stated "insects are essentially creatures of the 

 earth and air," but many species have adopted an aquatic life, 

 some to spend only their immature stages in the water, others 

 to linger there throughout most of their days, quitting it only 

 to extend the foraging grounds through flight. 



To this latter group belong the water bugs. It is the purpose 

 of this chapter to indicate some of the structural contrivances 

 possessed by these insects, and the manner in which they are 

 used. The chief modifications have taken place along the lines 

 of locomotion, prehension, and respiration, and under these 

 three heads the question will be discussed. 



In considering these various questions it is natural to treat 

 the subject from the standpoint of degree of adaptation. This 



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