1920] MetcalJ-0 shorn: Insects of Between-Tide Zone 115 



In his discussion of the special adaptations for survival under 

 submergence he cites the calcar as a structural modification 

 developed as a reaction to the tidal conditions. To appreciate 

 the absurdity of this inference it is only necessary to note that 

 this structure occurs in all species of Delphacinae and, in 

 many other species having no periods of submergence to con- 

 tend with in their habits there are fully as large and specialized 

 calcars. Arndt says: "The hoods on its feet, the greatly devel- 

 oped proximal segment and the spur are the peculiar modifica- 

 tions which determined that this leaf-hopper should inhabit this 

 particular region." In all these structures this species is in close 

 accord with the other members of the group. We must look 

 elsewhere for any real modifications of structure. 



It should be recognized that these insects and hosts of 

 related forms have been for ages adapted to clinging to the 

 stems and leaves of plants and well fitted for withstanding wind 

 and other forces that might tend to dislodge them. The essen- 

 tial factor that the new environment called for was adjustment 

 to submergence in water and this involves especially the abilit}^ 

 to hold sufficient quantities of air in or adjacent to the tracheal 

 system to carry over the periods of submergence. 



Libumia detecta VanD. ( = circumcincta VanD. micropterous form). 



This species of Delphacid occurred in great abundance on a 

 grass that grew luxuriantly near the level of low tide and where 

 there were enormous swarms of fiddler crabs. At this level the 

 grass must be completely submerged during high tide and for 

 much of the time during the rise and fall of the tide. It is evi- 

 dent, therefore, that the species both as nymphs and adults 

 and doubtless also in the egg stage must be successfully adapted 

 to survive long periods of submergence, several hours at a time 

 at least. The exact method of protection during this sub- 

 mergence could not be determined but from the shape of the 

 insect, both nymph and adult, it would appear that they can 

 crowd themselves into the spaces between leaf -sheath and stem 

 or into the furrows Of the leaf blades in such manner as to hold 

 their attachment to the plant, detachment from which would in 

 all probability mean disaster. 



It may be added that this species was not found at any point 

 above the between tide zone and therefore its adaptation to this 

 situation is evidently complete and it is probably restricted to 

 the species of grass which is confined to this habitat. 



