THE FUNCTIONAL ANATOMY OF THE MESOTHORACIC 
LEG OF THE WATERSTRIDER, GERRIS REMIGIS 
SAY (HETEROPTERA)* 
By Elizabeth Bowdan 
Department of Zoology, University of Massachusetts 
Amherst, Mass. 01003 
Introduction 
Gerris remigis is a heteropteran which spends most of the 
time on the surface of flowing streams. On the surface of the 
water it moves by rowing, during which the meso- and meta- 
thoracic legs, especially the former, sweep powerfully backwards 
pushing against the surface film of the water (Darnhofer-Demar, 
1968). In order to stand, the animal needs a large area of con- 
tact with the surface. Both standing and rowing require that 
these legs extend laterally consequently they differ from the 
more or less vertically orientated legs of most other insects, in- 
cluding many terrestrial Heteroptera. In a recent review of the 
evolution of Heteroptera, Popov (1971) discussed the divergence 
of the coxae in the infraorder Leptopodidomorpha — of which 
the Gerridae are members — in order to move on the surface of 
the water. It thus seemed interesting to compare these legs with 
those of Heteroptera having a different life style. Those Heterop- 
tera whose mesothoracic legs have already been studied in suf- 
ficient detail are Gelastocoris oculatus (Parsons, 1960) and Belo- 
stoma flumineum (Segal, 1962). Since these two insects belong 
to the Hydrocorisae, and since Gerris belongs to the Amphibi- 
corisae, Gelastocoris and Belostoma are not closely related to 
Gerris. Nevertheless, they provide an interesting comparison, 
especially since Gelastocoris is littoral, Belostoma is totally aquat- 
ic and Gerris is surface-living. 
The primary purpose of this study, therefore, was to explore 
the modifications of the mesothoracic leg in terms of the external 
anatomy, musculature and pattern of innervation and to relate 
*Note added in proof: In a recently published paper, N. M. Andersen includes 
a brief description of the functional anatomy of the mesothoracic leg of Gerris 
lacustris which accords well with that presented here for Gerris remigis. [Vidensk 
Meddr dansk naturh Foren, 1976, 139:337-396.] 
Manuscript received by the editor April 26, 1977 
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