Harper, Behavior of Corethra. 455 



8. The larvze are positively phototropic, when attuned to 

 out-of-door intensity, in the sense that they move horizontally 

 tov^ard light, but not upward. The pupae move in any direction 

 toward light of greater intensity. Freshly collected larvae gather 

 in the lower lighted corner of an aquarium with side illumina- 

 tion. The positive reaction changes to negative after a time. 



9. The larvae are armed with segmental sensory bristles and 

 also several pairs of chordotonal organs, and their orientations due 

 to mechanical stimuli and vibrations are their most marked forms 

 of response. The negative response may be accentuated by 

 repetition and intensification of the stimulus, and lead to contin- 

 uous movements of short duration, in a tolerably straight but zig- 

 zag path. 



10. The movements are powerful, since they may involve one 

 half of the musculature at each stroke. This compensates for 

 lack of momentum due to discontmuity of movements. Fatigue 

 is soon shown on continued mechanical stmiulation. Acclimati- 

 zation, distinct from fatigue, is shown. 



11. The function of the air sacs is static, enabling the main- 

 tenance of position at various levels in accordance with the physi- 

 ological state. They have a dynamic function in automatic 

 righting movements and in producing buoyancy at times. Their 

 respiratory function is undoubtedly of great importance in connec- 

 tion with their depth migrations. 



12. The behavior of the pupae becomes more conformed to 

 an ordinary type, with loss of transparency and acquisition of 

 special pupal organs. Movements are symmetrical and more 

 continuous. Reactions are more pronounced. 



Evanston, 1)1., 

 June 19, 1907. 



