Explanation of Plate XVI. 



Fig. 1. To show the fearlessness of the flies, ^lede Dacuii zonalus 

 on fingers very slightly smeared with methyl engenol. 



2. Male Dacus at methyl eugenol, eugenol, isoengenol, 

 and " methylate of isoengenol " (labelled methyl- 

 isoengenol). Small drops of the substances were 

 placed on paper. Practically all the Mies were typical 

 D. zonatus, but at the left-hand drop of isoengenol 

 there was one D. diver sus and one intermediate 

 D. zonatus-ferrugmeus. The neglect of the eugenol, 

 and isoeugenol by D. zonatus is very marked. 



