DEVELOPMENT OF COMPOUND EYE. 



reach their ultimate length. The four pseudocone cells are still to 

 be found in the vesicle formed by the supporting cells on the 

 seventh day. They lie immediately below the corneal facets which 

 have now become more decidedly plano-convex. No so-called 

 optic cup is present at this time, but an examination of the living 

 fly shows the beginning of the formation of pigment (Figs. 8 

 and 9). 



The eye is completed on the eighth day by the cupping of the 

 pseudocone, leaving the four pseudocone nuclei surrounding the 

 end of the rhabdome at the apex of the cone (Fig. 10). 



The adult leaves the pupal case on the ninth day. 



This brief resume of the ontogeny of the compound eye presents 

 some interesting problems in correlative development. Kopec, 

 1922, by the removal of the ganglia of the caterpillars of Lymantria 

 dispar L., after their last moult, showed an entire independence of 

 the development of the optic apparatus and the brain. In Dro- 

 sophila it has been shown, however, that the ultimate structure of 

 the eye is determined very early in larval life. The subsequent 

 removal of the brain would not be expected to influence further 

 development. The present study shows the forerunners of the 

 ommatidia to be structurally present on the fourth day of larval 

 life. 



That the nervous system and the dioptric system are closely cor- 

 related in their development is further shown by the striking re- 

 duction in the size of the optic ganglion in the bar-eyed mutant. 

 When compared with that of the full-eyed fly it is seen to be less 

 than half as great in diameter (Fig. n). 



SUMMARY. 



1. The cell groups, representing the primordia of the ommatidia 

 of the compound eye of Drosophila mclanogaster, have been found 

 in the four-day larva. 



2. The fusion of the imaginal disks and the supra-esophageal 

 ganglia take place on the third day of larval life. 



3. There is a correlation between the development of the nervous 

 system and the dioptric apparatus, as shown by the reduction in 

 the size of the optic tract in the bar-eyed mutant. 



