1955] 
Roth and Willis — Diploptera dytiscoides 
67 
parison with the nymphs of other species of cockroaches, 
even those with adults twice the size of the adult Diplop- 
tera. 
Mr. George Riser, formerly of our laboratory, working 
on the life history of Diploptera, has found that at 85 °F. 
eggs hatch about 58 days after the female has mated; al- 
lowing about a week after copulation for oothecal forma- 
tion, embryogenesis takes about 50 days. He also found 
that nymphal development took about 38 days for males 
(9 individuals) which molted only 3 times; females (13 
individuals) took about 50 days to mature and underwent 
4 molts. Molted skins are not eaten by nymphs or adults. 
We thank Dr. Harold Hagan for his interest and for 
critically reading the manuscript. 
Summary 
The eggs of the viviparous cockroach Diploptera dytis- 
coides absorb both water and solid matter from the female. 
During embryogenesis, dry matter in the eggs may in- 
crease about 50 times and the water content may increase 
about 85 times. In its embryonic development, Diploptera 
is unique among cockroaches in that the embryo gains 
solids from the mother in addition to the yolk initially 
present in the egg. 
In laboratory colonies, teneral females mate normally 
with older males. The ootheca is formed as in other species 
of cockroaches: the eggs are extruded from the oviduct 
and arranged vertically in an ootheca within the vestibule. 
Sometimes one egg (the first laid) may protrude beyond 
the end of the abdomen, but most of the eggs remain with- 
in the vestibule while the female rotates the ootheca and 
starts retracting it into her brood sac. 
The number of eggs per ootheca ranged from 9 to 13, 
with a mean of 11.4. Embryogenesis takes 50 or more 
days. The embryos hatch in pairs, being extruded head 
first from the female. Male nymphs took about 38 days 
to mature, molting 3 times; females became adults after 
about 50 days, molting 4 times. 
