578 
GENETICS: M. B. STARK 
Many flies have appeared with only one wing. In place of the missing 
wing a large tumor has developed as shown in figure 4. The offspring 
from these flies do not throw a greater number of one- winged flies than 
do their normal sisters. 
Microscopic examination of sections of the wing tumor reveals the 
fact that the wing disc had begun to develop but an ingrowth of the 
tumor cells had checked the development (figure 5). 
Fig. 5. A section through the wing tumor (fig. 2) showing ingrowth of tumor cells into 
the partly developed wing disc. 
Tumors have also appeared in place of the other appendages. In 
several, the fore-legs were missing, a tumor having prevented the com- 
plete development of the imaginal discs of the legs. These flies had 
difi&culty in balancing the body and did not live long. In many flies 
only one leg or only a portion of the leg would be displaced by a tumor. 
