OF WASHINGTON, VOLUME XVIII, 1916 175 



which were fully fed deserted the apple and pupated in the bottom 

 of the box. He suggested that their normal habit is to enter the 

 earth to pupate. In the maggot trap experiment mentioned 

 above, about 1300 larvae of this species were caught in the water 

 below the moist bran, as compared with 1430 larvae of the house 

 fly from the same medium. The bran was moistened and put in 

 the trap on June 9. The larvae of Muscina stabulans were the 

 first to appear in the water below. They were first caught on 

 June 15, and the migration ceased on June 21. House fly larvae 

 were first caught on June 17, and continued to appear until June 

 26. The larvae of Euxesta migrated during the period from June 

 21 to July 1. The experiment was ended at that time and there 

 were still a number of these larvae in the bran. The larvae of 

 Oplyra leucostoma first appeared on June 25, and some were 

 present when the experiment ended. 



This is an interesting sequence which at first thought would be 

 easily explained on the basis of differences in the length of the 

 larval periods, the larvae developing most rapidly being the first 

 to migrate. But it is quite possible that a close study of the exact 

 time when eggs were deposited would reveal some connection be- 

 tween the time of deposition and the particular stage in the pro- 

 cess of fermentation. In other words, different species of flies 

 are probably attracted to different combinations of decomposi- 

 tion products, and if all the chemical and biological changes that 

 take place in a fermenting mass such as moist bran, were known, 

 it might be possible to discover some correlation between such 

 changes and the sequence of the dipterous fauna. 



Neither the larvae of Euxesta nor of Ophyra were taken from 

 horse manure under the same condition as the bran. Horse 

 manure has of course undergone destructive changes before 

 evacuation from the alimentary canal, and the remaining stages 

 of fermentation are passed through rapidly. These facts suggest 

 that only those flies with a short larval period are adapted for 

 life in this quickly fermenting medium, and that those with a 

 longer larval period seek out substances which change more slowly 

 in which the destructive processes have to begin from the begin- 

 ning, as it were. 



EXPLANATION OF PLATE xn. 



Fig. 1. Full grown larva of Euxesta notata as seen from the left side 

 X 14. 



Fig. 2. Cephalopharyngeal skeleton of mature larva, indicating more 

 highly chitinized parts and the longitudinal folds in the ventral wall of 

 the pharyngeal schlerite. Outlines by camera lucida after treatment 

 with KOH. X 100. 



