574 
GENETICS: M. B. STARK 
Star is located in the second chromosome and that for dichaete in the 
third chromosome. In the F2 generation tumors reappeared as frequently 
among the star as among non-star flies. On the other hand none of 
the dichaete flies had tumors. This result indicates that one at least of 
the genes essential for tumor development is in the third chromosome 
closely linked to dichaete. To locate the gene at a definite locus in the 
third chromosome, flies with tumors were mated to dichaete ^hairless/ 
In the back crosses, no crossing over between the tumor and dichaete 
was obtained, while the crossing over between the tumor and hairless 
was the normal amount, 25%. The gene of the tumor is thus shown to 
be very close to that of dichaete which is at about 11.7 (table 1). The 
expected number of tumor bearing flies in the back cross is 50%. As 
seen in table 1 not more than 5% developed the tumor. This indicates 
TABLE 1 
DATE 
WILD TYPE 
HAIRLESS 
DICHAETE 
HAIRLESS 
DICHAETE 
HAIRLESS 
TUMOR 
9 
9 
cf 
9 
cf 
9 
cf 
9 
9 
13 
13 
26 
24 
7 
5 
10 
5 
0 
2 
1 
0 
28 
25 
58 
54 
9 
7 
14 
9 
2 
3 
3 
0 
July 10, 1918 
37 
27 
28 
20 
4 
3 
5 
5 
4 
3 
1 
1 
17 
16 
19 
17 
3 
4 
9 
5 
2 
2 
0 
1 
16 
14 
26 
20 
4 
2 
4 
4 
2 
1 
1 
0 
32 
38 
30 
26 
14 
16 
20 
18 
4 
5 
2 
0 
Total 
143 
133 
187 
161 
41 
37 
62 
46 
14 
16 
8 
2 
Crossing over between tumor and hairless = 10/40 = 25%. 
that more than one gene is concerned with the inheritance of the tumor. 
Further investigations of this point are being made. 
2. Position of tumor in larva. — To determine the time of appearance 
of the tumor and its position in the body 208 larvae were isolated and 
examined for tumors. Tumors were found in 180 of these (table 2). 
They seem to occur more often in the twelfth and thirteenth segments, 
occurring in the twelfth 97 times and in the thirteenth 72 times. Two 
tumors were observed in each of thirty-eight larvae. Twenty-seven of 
these cases had the tumors in different segments and eleven in the 
same segment. One larva had three tumors. Twenty-five larvae with 
tumors had in addition smaller tumors which were regarded as metas- 
tases. These when very small are often carried into the heart with 
the blood and there develop into narrow elongated tumors as shown in 
figure 1. 
