340 DAVID DAY WHITNEY 
In some of the experiments the eggs of the females from ‘the 
different races were counted at frequent intervals in order to 
determine whether all the females of the various races produced 
the same number of eggs in the same period of time. This was 
not found to be the case for the females of some of the races pro- 
duced eggs faster than the females of other races but as the eggs 
of all females of all races hatched in about the same length of 
time after they were laid, the rates of reproduction were deter- 
mined by counting the young females in a dish with their mother 
after a definite period of time had elapsed since the mother was 
first isolated. 
The first series of observations were made during the period 
in which race B was becoming extinct. Many young partheno- 
genetic females of approximately the same size were isolated from 
each of the four races at the same time, placed under identical 
external conditions and their rates of reproduction recorded. 
Table 1 shows the general results. Race B was unmistakably the 
weakest in that only one female out of sixty isolated was able to 
live and reproduce, while twenty others lived the normal length 
of time for individuals of the race, but never laid any eggs. 
These twenty females developed and produced many eggs in their 
ovaries but never laid them. The eggs remained inside the body 
of the female and ultimately seemed to fill the entire animal, 
crowding and concealing all the internal organs from view. After 
a time some of these eggs were observed to start development into 
embryos; but soon the embryos died and many of the egg mem- 
branes ruptured and the body of the female became filled with 
a mass of egg materials from the broken and decomposing 
eggs. These females finally became larger than normal females; 
due to this accumulation of unlaid eggs which crowding out 
the wall of the animal caused the large size. Such females are 
designated as sterile females. Thirty-nine of the remaining 
females did not live to maturity probably because of their weak 
condition. In race A forty-six of the young females matured and 
produced daughter-females at a higher rate than the one female 
of the Brace. In race C fifty-three of the young females matured 
and had a higher reproduction rate than either of the races A 
