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Photos by] F- [J. J. Ward, FBS. 
HEAD OF HYDROMETRA. HEAD OF‘: GERRIS. 
The heads of these two Skaters, enlarged to twenty-five times the natural size, are shown side by side for comparison. In Gerris the dagger-like tongue is shown extended 
in front of the head, but in Hydrometra it is folded underneath, out of sight. Note the respective lengths of the head and position of the eyes. 
