THYSANOPTERA AND ORTHOPTERA. 197 



lighted directly from the window some 8 or 9 meters away. A bag con- 

 taining a number of thrips was opened and set in the darkened room 

 near the farthest wall. The tlirips were not disturbed, so that they had 

 opportunity to arrange their wings for flight. Four minutes later the 

 window was carefully examined and the thrips counted. The results 

 are given in Table III below. These rooms were not used for labora- 

 tory purposes, hence it is not probable that any thrips other than those 

 confined in the bag were afterwards found at the window. One speci- 

 men was found on the outside of the glass, wher^ it might easily have 

 crawled through broken glasses or other holes, so that the number of 

 thrips found at the window may not be complete. The exi^eriment 

 was repeated another day, after making sm'e that there were no tlirips 

 on the window pre\dousl5^ to releasing those in the bag. Both counts 

 are given in the table. The numbers in the third column are computed 

 on the assumption that, were the insects not attracted by the light, they 

 would fly along approximately horizontal lines in all directions from the 

 starting-point. 



TABLE III. — Showing the number of individuals of Euthrips tritki which 

 flew to a window 8 or 9 m. distant, probably at a single flight. 



Approximate number Number of thrips Number which should, by 



of thrips in the found at window the laws of chance, have 



bag. after -i minutes. reached the window. 



120 12 2.2 



45 6 0.86 



The numbers show conclusively enough, I think, that this species of 

 thrips is positively phoiotactic. But the point I wishio make here is 

 that these specimens must have gone to the window b}- a single flight, 

 a distance of 8 or 9 meters. 



Studies of the thrips on Rush Lake seem to give evidence of longer 

 flights. Rush Lake is an old hollow lying landward of the first sand 

 dune to be thrown up, that is, the one farthest from Lake Hm-on, It 

 is being gradually filled up, and much of the bottom is now very soft 

 ooze formed of decaying plant material. In this the pickerel weed 

 (Pontederia cordata) is one of the most common plants. In some 

 places it grows in great patches in which the plants are not over a few- 

 inches or at most a few feet apart. Elsewhere there are isolated clumps, 

 separated from all other vegetation by as much as a hundred meters 

 or more. These plants die down beneath water in the winter, so that 

 no thrips can hibernate on them. Any specimens, therefore, that are 



