GENETICS: M. B. STARK 
575 
The tumor may develop in the early or in the late larval stages. 
Fully developed tumors have been found in two-day old larvae and 
very young tumors in four-day old larvae. Of the 208 larvae isolated, 
only 32 were without tumors. Tumors must have developed later in 
these individuals since all of the flies that emerged from them had 
tumors. 
One hundred and seventy-six flies emerged from the 208 larvae 
isolated, approximately the same percentage as in the control experi- 
ment in which 200 larvae from a normal stock were isolated, of which 
170 emerged as flies. 
TABLE 2 
POSITION OF TUMORS 
IN SEGMENTS 
NUMBER OF 
LARVAE WITH 
TUMORS 
NUMBER WITH 
ONE TUMOR 
NUMBER WITH 
TWO TUMORS 
NUMBER WITH 
THREE TUMORS 
NUMBER WITH 
METASTASES 
14 
5 
5 
14-13-12 
1 
1 
13 
49 
44 
5 
6 
13-12 
16 
16 
4 
13-11 
2 
2 
13-10 
1 
1 
13-8 
3 
3 
12 
75 
65 
10 
12 
12-11 
4 
4 
1 
12-8 
1 
1 
1 
11 
8 
6 
2 
9 
9 
9 
8 
5 
5 
6 
1 
1 
1 
Total 
180 
135 
88 
3 
25 
Total number of larvae, 180. Total number of tumors, 226. Total number of metastases, 36. 
3. Development of tumor. — The structure of the tumor in an early 
stage in its development in the larva is shown in figure 2. The cells 
are rounded or polygonal in shape and contain pigment. As the tumor 
grows older the amount of pigment increases, the cells filled with it 
become crowded towards the periphery and flattened as shown in 
figure 3. 
The tumor takes its origin in groups of cells similar in structure to 
the cells found just inside of the hypodermis of the larva. These cells 
are originally derived from the hypodermal cells. In the fly the tumor 
when fully matured is entirely permeated by pigment and is black in 
color. The cells have stopped increasing in number. As the fly grows 
older the tumor tends to shrink in size but does not disappear. 
