518 MARY B. STARK 



sterile Locke's solution. All the ordinary laboratory media were 

 inoculated by this suspension and incubated under both aerobic 

 and anaerobic conditions. No growth appeared. The sterile 

 egg suspension was also mixed with the sterile media upon 

 which stocks of flies without tumors were reared. The larvae 

 that fed upon this food contaminated with the egg suspension 

 developed normally. 



The suspension was also injected into adult flies. The flies 

 that survived the operation continued to live ari,d to produce 

 normally. The egg is evidently not the source of infection. 



DEVELOPMENT OF THE TUMOR 



Tumors have been found to occur in various regions of the 

 body of the larva. Whether it occurs more often in any par- 

 ticular region has not yet been definitely determined. Sections 

 of larvae show, however, that the tumor occurs in embryonic 

 tissues destined to build up the adult organs during the pupa 

 stage. These tissues are spoken of as i^iaginal disks and imagi- 

 nal rudiments. 



In the dorsal region of the thoracic segments of the larva there 

 are six groups of embryonic cells or imaginal rudiments in which 

 the tumor may take its origin. Figure 3 shows a tumor de- 

 veloping in the two anterior rudiments. Figure 4 shows the 

 tumor developing in the posterior rudiment. In the early 

 stages of the development of the tumor the cells of the imaginal 

 rudiment begin to deposit pigment. As development goes on, 

 there is a tendency for the pigment cells to be pushed toward 

 the periphery by the rapidly proliferating cells of the rudiment 

 and there become deposited in laminated layers, as shown in 

 figure 3. Figure 4 shows the entire rudiment encapsulated by 

 the pigmented, flattened, peripheral cells and entirely separated 

 from the other rudiments. The laminated layers of flattened 

 cells may again be surrounded by proliferating cells, as shown 

 in figure 4. 



The tumor may also develop in the ganglion of the proventric- 

 ulus. This ganglion consists of a number of large cells very 



