I 
However, of the 21 litters born during the spring 
of 1949 and surviving to the time of termination of 
the colony in May 1949, 20 of these were born to 
females of the line having the closest affinities to 
the Southeast side of the pen. It is also interesting 
to note that the one remaining litter was born to the 
only female of the second line who, herself, was 
born on the Southeast side of the pen. The impor- 
tance of these observations and those which immedi- 
ately follows, is that among these Norway rats only 
a segment of the population successfully repro- 
duced. Thus there should result a more rapid 
development of genetic homozygosity than would be 
anticipated purely on the basis of random breeding. 
Dispersal of males from their place of birth (pp. 
170-171; table 30), particularly the dispersion 
of males from the Southeast group to the North- 
west group, might be considered as preventing the 
more rapid development of homozygosity. This 
situation does not vitiate the former conclusion 
since the females with which these displaced males 
Table 30. — Relationship between place of birth and place of later residence (i.e. migration) 
! 
Place born (1948) 
Total born in 1948 
Place found May 1 949 
Southeast half of pen 
Northwest half of pen 
Male 
Female 
Total 
Male 
Female 
Total 
Male 
Female 
Total 
Southeast half of pen 
11(a) 
18(a) 
29(b) 
0 
0 
0(b) 
11 
18 
29(c) 
Northwest half of pen 
26(a) 
10(a) 
36(b) 
15 
16 
31(b) 
41 
26 
67(c) 
Total 
37 
28 
65(c) 
15 
16 
31(c) 
52 
44 
96 
Comparison 
a. Sex difference in place of residence during May 1949 of rats born in Southeast side of Pen 
b. Tendency to leave home in relation to Place of Birth 
c. Redistribution of the population between 1948 and 1949 
!l 
Table 31. — Reproduction during spring of 1949 in relation to place of birth in 1948 and place of residence in May 1949 
Place born, 1948 
Place residing, May 1949 
With 
litters 
Without 
litters 
Chi 
Square 
P 
Southeast side of pen 
Southeast 
14 
4 
6. 518 
0.01 
Northwest 
5 
5 
. 021 
. 80 
Northwest side of pen 
Southeast 
0 
0 
Northwest 
2 
14 
7. 941 
. 01 
Total 
21 
23 
Expected ratio 
. 477 
. 523 
141 
I 
Tests of significance 
Chi Square 
P 
6. 348 
0.02 
23. 215 
. 01 
25. 531 
. 01 
came into association, produced essentially no 
surviving progeny. 
By taking into consideration the genealogical 
record and certain other data regarding repro- 
duction, survival, and migration, it is possible to 
gain a picture of the fate of the colony with refer- 
ence to its two main lines of descent. These data 
are shown in tables 29, 30, and 31. 
Table 29. — Survival of rats weaned during 1948 
Survived 
less than 
150 days 
Survived 
more than 
1 50 days 
Total 
Southeast born: 
105 
Died before May 1949. 
20 
20 
Alive May 1 949 
65 
Northwest born: 
66 
Died before May 1 949 . 
14 
21 
Alive May 1 949 
31 
