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strong legs, which are conducive to swift- movements and which give them 

 the designation of running spiders, make them especially titted to inhabit 

 a zone in which safety may lie in retreat. 



The terrestrial conditions which prevail for one-half of the time in 

 the between the tides zone, make it necessary that the permanent inhabi- 

 tants of such a zone be insects which breathe not by means of gills, but 

 that they be air breathing insects. Terrestrial conditions are the normal 

 ones for their activities. They are inactive during the high tide, or the 

 period of submergence. The most striking phenomena is the strictly zonal 

 distribution of the insects of the between the tides zone. Each species 

 is undoubtedly specialized in some way to fit it to inhabit this area, and 

 this specialization has rendered it incapable of surviving in other zones. 

 Even the Megamelus marginatus, which travels with comparative rapidity, 

 never migrates to the Juncus areas. To determine the exact reasons why 

 the insects of this zone cannot survive in the higher areas of the salt 

 marsh, more extensive studies of their life histories and habits must be 

 made. Further observations concerning these features, I believe, will 

 add much to the already extensive and fascinating data relating to 

 adaptation among insects. 



Purdue University, 

 Lafayette, Ind. 



