THE MIGRATION OF THE FLY LARVAE 313 



sorts. When it reaches the tip of the leaf, it stops and appar- 

 ently surveys the ground for a while, then getting by chance 

 into another groove, it starts downward. Once on this course 

 it works its way down in the same manner as the larva which 

 came from an egg deposited in the normal manner. The behavior 

 of the larvae hatched on the lower surface of the leaf is essen- 

 tially similar to that of those on the upper surface. There was 

 a tendency among the larvae from eggs laid in an inverted posi- 

 tion on the lower surface to get over to the upper surface after 

 they have gone up the leaf for some distance. 



Rate of Migration. — Individual differences influence the rate 

 ■of migration more than physical factors, such as the degree of 

 inclination of the leaf, temperature, humidity, mechanical ob- 

 structions, and the like, although these factors always enter 

 into the problem and need to be taken into consideration. The 

 larvae which came from eggs laid in succession by the same 

 female on the same leaf and in juxtaposition may not be able 

 to move at the same speed. As a matter of fact, none of the 

 larvae under observation moved according to any set of arbi- 

 trary standards. Tables I and II show the rates of migration 

 of larvae when the eggs are deposited normally and when they 

 are deposited in an inverted position. 



TABLE I 

 Rate of Migration of Larvae Hatched from Eggs Laid in Normal Manner 



Average time Average 



required to distance 



move 1 mm. traveled 



Total No. of larvae 205 4 min. 36.4 sec. 51.5 mm. 



No. of larvae that got down 



into sheath 157 4 min. 1.6 sec. 53.3 mm. 



No. of larvae died on leaf 48 6 min. 30.6 sec. 45.5 mm. 



TABLE II 

 Rate of Migration of Larvae Hatched from Eggs Laid in Inverted Position 



Average time Average 



required to distance 



move 1 mm. traveled 



