Psyche 
[December 
1 68 
In the parthenogenetic strain the first ovulation occurs when the 
female is about 13 days old whereas the second ovulation takes place 
about 16 days after birth of young. This 3 day difference is explained 
by the difference in size of the oocytes in the newly-emerged female 
and in the female at parturition ; the oocytes are smaller after the 
female gives birth and it takes about 3 days to attain the same degree 
of development as they are at adult emergence. In Diploptera the 
reverse is true and the second preovulation period is 3 days shorter 
than the first although, as in Pycnoscelus the growth rate of the 
oocytes is about the same during the first and second preovulation 
periods. In Diploptera the oocytes at parturition are about the size 
of those of a 3-day-old mated female which explains the shorter period 
required for ovulation after parturition (Engelmann, 1959). 
Pycnoscelus surinamensis 
Fig. 1. Ovarian cycle of Pycnoscelus surinamensis (parthenogenetic strain). 
Each point on the curve for oocyte development from 0 to 13 days is the 
mean of 6 to 13 measurements (N — 134). Each point for the gestation period 
from 13 to 68 days represents individual measurements (N = 99; when 2 or 
more points were similar for a particular age only one is indicated). The 
part of the curve representing the growth of the oocytes after parturition 
(birth) is based on 1 to 3 individuals (N — 24) for each point. Vertical bars 
— standard errors of mean values. 
In the parthenogenetic strain of Pycnoscelus it is obvious that mat- 
ing is unnecessary for development of the oocytes. The initial develop- 
ment of the oocytes in the bisexual strain is similar to that found in the 
parthenogenetic form but differs in that mating slightly stimulates the 
growth rate and also is necessary for normal retraction of the ootheca 
into the uterus. Mating a parthenogenetic strain female with a male 
