LIFE CYCLE OF HYDATINA SENTA 293 
in the proportion of male-producers, such that a comparison of 
two lines may show fewer male-producers in the older line, 
although the two lines would have been equal had each been taken 
at the same number of generations after the fertilized egg. An 
application of this discovery is found in the present experiment. 
The original line in this experiment is line 8 of table 1. It will 
be seen in that table that the early generations of the line had a 
larger number of male-producers than the subsequent genera- 
tions. The original line passed through ten generations before 
the inbred line started. If these ten generations, comprising 
147 male-producers and 315 female-producers, be added to the 
27 generations given in table 2, then the total for the original line 
shows 18.2 per cent of male-producers, or a higher percentage 
than that of the inbred line. We may not be justified in including 
the first ten generations, as I have just done, but in view of the 
decrease in the proportion of male-producers in the later genera- 
tions, it seems to me unsafe to ignore the early generations. 
Incidentally it may be mentioned that the average size of family 
in the entire original line, exclusive of the last two families which 
were not fully recorded, was 34.5 as compared with 30.7 in the 
inbred line. 
Experiment 2. Twice inbreeding. Females of the inbred line 
of the preceding experiment were paired with males of the same 
line. Of 144 eggs obtained, one hatched November 26, and 
became the parent of the line in table 3 designated ‘twice inbred.’ 
This line is compared with those parts of its parent (also inbred) 
line and the original (‘grandparental’) line that were reared at the 
same time. 
Here the difference between the two inbred lines is not great, 
while the percentage of male-producers in the original line is con- 
siderably less. Since all three of the lines are at different ‘ages,’ 
that is, a different number of parthenogenetic generations has 
been passed through in each line since the fertilized egg from which 
the line was derived, it is of interest to note the proportion of 
male-producers in the whole lines, and not merely those parts 
that were bred simultaneously. In the original line, including 
28 generations reared previously to the beginning of this experi- 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 12, NO. 2 
