LIFE CYCLE OF HYDATINA SENTA 303 
the exception of three eggs that hatched in less than twelve hours) 
was hatched, and the young reared to maturity in manure solu- 
tion. That the manure solution used was strong enough to ex- 
clude male-producers was shown by rearing five successive gener- 
ations in it. These five generations comprised 185 individuals, 
all female-producers, while the sister line in spring water, as shown 
in table 7, included many male-producers. 
TABLE 7 
Showing number of male- and female-producers in two series of generations bred 
from sister individuals of Hydatina senta, in one of which the eggs were laid and the 
young reared to maturity in spring water, in the other the eggs were laid in spring 
water, but hatched and the young reared to maturity in manure solution. 
HATCHED AND REARED IN SPRING WATER | HATCHED AND REARED IN MANURE SOLUTION 
Date of first Date of first 
| Number of Q| Number of 9 @ Number of o&'9) Number of 2 9 
young | young 
February | February 
8 25 15 | 8 9 38 
9 19 30 | 9 38 9 
11 8 31 | 11 13 26 
12 18 31 | 12 7 | 33 
ae A ae ee ey) | i} = . 
Movale.. ee 70 107 | 67 106 
Per cent of 
oe 39.5 | 38.7 
If the nature of a female is not determined before the twelfth 
hour of the egg stage, the treatment just described should exclude 
male-producers from the one line. If the nature of a female is 
determined at some time between the first and twelfth hours of 
the egg stage, the treatment described should cause a reduction 
in the proportion of male-producers in the one line; and the later 
the determination occurs, the greater should be that reduction. 
From table 7 it appears that the young rotifers reared, from the 
egg stage on, in manure solution, comprise approximately as many 
male-producers as those reared in spring water. The fact that 
there is little or no reduction in the proportion of male-producers 
in manure solution seems to indicate that the nature of the female 
