44 



would seem sufTicienUy explained by the lonely situation of the 

 feniale rufoscutellatus — a remigis maie was acceptable « faute de 

 mieux » ; and we may conclude that in the Gerrids isolation of the 

 species dépends not on rigid anatomical incompatability but rather 

 on more plastic psychological faclors, which are sufficiently com- 

 pelling under ordinary circumstances but may weaken in tlie face 

 of adversitv. 



