42 A7mals Entomological Society of America [Vol. X, 



Light Relations. — No attempt has been made to carry on 

 refined experiments on the behavior of these flies. However, 

 observations and some rough field experiments were made on 

 the relation of //. confluens to light, the results of which will be 

 given in brief form. 



A study of the habits of these flies in the field has shown 

 that they are active during the day and are found in large 

 numbers on the upper surfaces of the floating water-lily leaves. 

 Very few were observed in any other situation. It thus appears 

 that since the water-lilies grow in maximum exposure to sun- 

 light and are never shaded, the flies prefer well-lighted condi- 

 tions and positive phototaxis is suggested. A number of 

 experiments were made by placing various lots of flies in a glass 

 tube, closed at both ends and equipped with a close-fitting cover 

 of heavy, black paper which enveloped about one-half of the 

 length of the tube, other conditions remaining unchanged. By 

 placing this tube in various positions with reference to the light 

 and reversing it after certain intervals of time, the reactions of 

 the insects could be noted. Irrespective of the position of the 

 tube, the flies reacted positively to the light by seeking actively 

 the uncovered end of the tube. These tests were repeated many 

 times with the same results. The migration from one end of the 

 tube to the other as the latter was reversed was continued over 

 and over again without any appreciable change in the character 

 of the response. Frequent use was made of this response in the 

 collection of flies for other purposes and in the transference of 

 individuals from one vial to another or from one breeding jar 

 to another. While no experiments were carried on in order to 

 determine w^hether any difference exists in the reaction by the 

 different sexes, collections of flies from the top surfaces of the 

 water-lily leaves, taken at random, showed no noteworthy 

 difference in the number of males and females. 



In the earlier paper, the writer ('14, p. 144) pointed out the 

 probable method of oviposition by the female, namely, passage 

 into the water on the under surface of the leaf and down the 

 petiole to the places where the eggs occur. The discovery of the 

 eggs makes this assumption all the safer. It thus appears that 

 although the female is distinctly positive in reaction to light, 

 this positive phototaxis is overcome by the stimuli inducing 

 oviposition since the passage into the water is accompanied by 

 a reduction of the light. Furthermore, the positive reaction to 



