THE MIGRATION OF THE FLY LARVAE 



317 



due to the inclination of the leaf, usually is not appreciable; 

 and even if it were of appreciable magnitude, it is better inter- 

 preted in terms of individual differences rather than due directly 

 to any difference in the inclination of the leaf. 



Variations in the Rate of Migration. — Every larva has a more 

 or less different average speed from any other larva. Each larva 

 has different speeds at different stages of migration. This varia- 

 tion in rate of migration in individual larvae can be seen in 

 figures 2 and 3. 



f\e \f\. "Vrv \ t\ ut t v 



Fig. 2. — Chart showing the distance traveled and the rate of migration of six larvae 

 hatching from eggs laid in the normal position. The dots indicate the loca- 

 tion of the larvae at the time of observation. 



As is shown in the figures, there seems to exist no regularity 

 in the rate of progress in individual larvae. They may move 

 faster at the beginning or toward the end of migration, or they 

 may move fastest at the middle of the journey. Again, they 

 may move for some time and then rest for an interval of from 

 five or ten minutes to twelve hours or more. 



Behavior of the Larvae on Migration. — The exact manner of the 

 locomotion of the larva is hard to observe because of the minute 

 size and the opaqueness of the wheat leaf. The larva seems to 

 move in somewhat the same fashion as other footless insect 

 larvae. The muscle tension coupled with the moist integument 

 bearing intersegmented grooves and the rather rough, hairy 

 condition of the creases of the leaf seem to operate in assisting 



