184 
Psyche 
[December 
surinamensis — parthenogenetic strain mated to males of the 
bisexual form). 
From the preceding summary one finds two extremes of dependence 
upon mating for stimulation of the corpora allata. In Diploptera , the 
majority of females require mating for maturation of the oocytes and 
its effect is the most striking since ovulation occurs about 10 days 
after mating, whereas virgin females may go for months without ovi- 
positing or they may never do so (Engelmann, 1959, i960; Roth and 
Stay, 1961). At the other extreme is the parthenogenetic strain of 
Pycnoscelus surinamensis where mating is unnecessary and the oocytes 
mature in virgins about 13 days after emergence. In this species some 
newly-emerged females already may have yolk in their oocytes. Be- 
tween these two extremes are species which show varying degrees of 
dependence on external mating stimuli for overcoming inhibition of 
the corpora allata. The oocytes in virgins grow but unless mating 
occurs the ovarian eggs do not mature and may degenerate before 
reaching ovulation size. This is particularly true in Nauphoeta, 
Byrsotria, and Blaberus giganteus and apparently in these species the 
corpora allata in many virgin females secrete an insufficient amount of 
hormone for the oocytes to mature; and in many of these females the 
partly developed oocytes are not maintained but degenerate unless the 
corpora allata are stimulated by mating. 
Various species show different degrees of dependence on mating for 
normal formation and retraction of the ootheca into the uterus. This 
is of particular interest, for the ability of virgin females to place the 
ootheca in the brood sac is a prerequisite to the evolution of partheno- 
genesis in false ovoviviparous cockroaches (Roth and Willis, 1961). 
Not all females of a species behave similarly which explains why some 
forms are included in more than one category in the above summary. 
It is this variation in behavior which may make possible the evolution 
of parthenogenesis in bisexual species of cockroaches. From the few 
species studied one can arrange the forms in a series to show the gradu- 
al evolution of retraction of the ootheca into the uterus in virgin 
females, although we do not imply that one gave rise to the other. 
Almost invariably in the bisexual strain of Pycnoscelus surinamensis 
the ootheca is dropped at formation in virgins. In Nauphoeta the 
ootheca is dropped at formation, partly retracted, or completely re- 
tracted. In Blaberus craniifer the ootheca is usually only partly 
retracted into the uterus. In Byrsotria the ootheca of virgins that 
ovulate is usually normally retracted into the brood sac. Although 
parthenogenesis is uncommon in false ovoviviparous cockroaches 
(other than the parthenogenetic strain of Pycnoscelus) it does occur 
