240 T. H. MORGAN. 



The four classes of females were realized in the results, but 

 only four of the possible eight classes of males appeared. These 

 four are the non-cross-over classes between spot and white; those 

 absent are the crossovers. Considering the small numbers in- 

 volved, the absence of these four classes of males is a probable 

 event. 



EXPLANATION OF PLATE I. 



FIG. i. Normal abdomen of male, dorsal view. 



FIG. 2. Ditto, side view. 



FIG. 3. Spot abdomen of male, dorsal view. 



FIG. 4. Ditto, side view. 



FIG. 40. Thorax (dorsal view) of young spot black showing dot and dash. 



