1962] 
Roth and Stay — Cockroaches 
205 
sure exerted in the uterus by the growing eggs (or by an implant into 
the uterus). In his more recent work (i960) Engelmann found that 
nerve cord severance did in fact result in renewed growth of the 
oocytes in pregnant females and that nervous stimuli are primarily 
responsible for inhibition of the corpora allata during pregnancy. 
However, he found a statistically significant delay of egg maturation 
after severance of the nerve cord, compared with animals from which 
egg cases were removed (35.2=1=0.7 versus 39.1 ±1.4 days in animals 
operated on 29 to 37 days after ovulation; 64.7=1=1.9 vs. 73.4=1=1.5 
days in animals operated on o to 1 day after ovulation). He concluded 
that other factors play an important role in inhibiting the corpora 
allata during pregnancy. By injecting O.i ml. of clear supernatant 
fluid from homogenized uterine eggs every fifth day for 30 days, he 
inhibited the corpora allata of Leucophaea. However, the injection of 
muscle homogenate resulted in a similar inhibition and Engelmann 
suggested that a non-specific substance inhibited the corpora allata 
during pregnancy. 
Although Engelmann has shown a delay in ovulation in females 
that had nerve cords cut compared to females from which oothecae 
were removed and has demonstrated that extracts of uterine eggs and 
muscle tissue have an inhibitory effect on the corpora allata, he has 
not demonstrated that there is a substance normally produced by the 
uterine eggs which acts to inhibit the corpora allata. Our experiments 
do not corroborate Engelmann’s finding that a substance from uterine 
eggs inhibits the corpora allata. We find that removing eggs from the 
uterus and implanting them into the abdomen (in Rycnoscelus, Byrso- 
tria, Blab eras craniifer and Leucophaea ) removed inhibition of oocyte 
-development, i.e. oocytes developed in the ovaries. We also find that 
cutting the nerve cord of pregnant females allows the oocytes to 
develop in the ovaries of Rycnoscelus , Byrsotria, Blaberus craniifer , 
and B. giganteus; we therefore conclude that the inhibition of the 
corpora allata during gestation, in these species at least, is dependent 
upon nervous stimuli resulting from the presence of the egg case in 
the uterus. 
Engelmann (i960) concluded that in Leucophaea the inhibitory 
influence of the ootheca may act on the last abdominal ganglion either 
by nervous or chemical factors and that there was “no reason to 
believe that the presence of an egg case in the brood sac is mechanically 
recorded in the brain (Roth and Stay, 1959). The question is still 
undecided.” Our conclusions in the 1959 paper were based on studies 
of Rycnoscelus surinamensis and Blattella germanica. In the parthen- 
ogenetic strain of Rycnoscelus there is no inhibition of corpora allata 
