THE MIGRATION OF THE FLY LARVAE 311 



the leaf during oviposition, instead of moving down toward the 

 base of the leaf as the larvae were ordinarily known to do, 

 moved up toward the tip of the leaf. In order to see if this 

 seemingly abnormal behavior was merely accidental or really of 

 regular occurrence, the following experiment was performed: 



A young wheat plant was held in an inverted position and a 

 female was allowed to oviposit on it. After the eggs were laid, 

 the plant was turned right side up and kept under observation 

 for the hatching of the eggs. Emergence occurred on the third 

 day and the larvae turned away from the base of the leaf and 

 moved up toward the tip of the leaf. This simple experiment 



Fig. 1. — Hessian fly larva hatching from egg and turninp toward posterior end. 



was repeated a number of times and the result was always the 

 same. Then the test was made with a number of modifica- 

 tions. In the first place, the influence of the orientation of the 

 egg itself on the subsequent orientation of the larva was to be 

 tested. In order to do this, it was necessary to have the eggs 

 laid in as wide a variety of ways as possible, keeping in mind 

 the possibility of such occurrence out in nature. Barring the 

 minor modifications, there are three distinct ways in which eggs 

 may be laid: (1) The eggs may be laid with their anterior end 

 pointing toward the tip of the leaf. This is what happens in 

 normal situations when the female stands on the leaf with her 

 head toward the tip of the latter. Since this mode of oviposi- 

 tion by Hessian fly is the most general out in nature, and since 

 this is the most natural way of ovipositing under ordinary cir- 

 cumstances, it will be designated in this paper as normal. (2) The 

 eggs may be laid with their anterior end toward the base of the 

 leaf. This is the .situation exactly opposite to that of the first, 

 and, undoubtedly, is of rare occurrence in nature. • Only under 

 forced conditions, and then with difficulty, will the female at- 

 tempt to lay eggs while in an inverted position. Many such 



