60 
Psyche 
[June 
And yet, morphologically, the reproductive system of Dip- 
loptera is comparable to that of Blatta orientalis, although 
some of the structures in Diploptera have become modified 
with its altered physiology (Hagan, 1941). 
TABLE l 
Changes in wet weight, water, and solids of the eggs of several species of 
cockroaches during embryogenesis 1 
Species 
Factors by which initial weights changed, 
per egg 2 
Wet weight Water Solids 
Blatta orientalis 3 
1.21 
1.35 
0.96 
Blattella vaga 
1.12 
1.32 
0.81 
Blattella germanica, 
1.21 
1.49 
0.74 
Nauphoeta cinerea 
2.11 
4.62 
0.81 
Diploptera dytiscoides 
73.47 
85.80 
49.28 
Of all the viviparous cockroaches, Diploptera is the most 
highly evolved : the oothecal covering is reduced, and the 
small size and number of eggs and the comparatively large 
size of the vestibule apparently make it possible for the 
female to transfer the ootheca into her brood sac without 
exposing the majority of eggs outside her body. Strictly 
speaking, Diploptera may be the only known case of true 
viviparity among cockroaches, in that the eggs are ap- 
parently rarely extruded beyond the vestibule and the 
embryos derive nourishment (other than yolk or water) 
from the female. 
Biological Observations 
We have frequently observed courtship and copulation. 
'The data for species other than Diploptera were computed from 
Roth and Willis (1955). 
2 Except for B. orientalis (see footnote 3), the weights of the oothecae 
were included in the computations, and therefore the actual changes 
would be somewhat larger; the youngest eggs had been recently deposited 
and the oldest were about ready to hatch. Factors less than unity in- 
dicate a decrease in weight. 
3 Based on eggs removed from the ootheca; the youngest eggs were 
11 days old and the oldest 32 days old (about 1 week prior to hatching), 
so that the changes might have been somewhat higher if recently laid 
and fully developed eggs had been used. 
