1967] 
Roth — Rotation of the Ootheca 
99 
Number of Female Offspring Rotating: 
Fejnale No. 
Left 
Right 
Mated to <$ A 
1 
0 
15 
3 
0 
35 
5 
1 
24 
Mated to <$ B 
6 
0 
18 
7 
1 
4 
8 
0 
8 
9 
0 
24 
10 
0 
17 
1 1 
2 
8 
These experiments are still in progress but it is clear that if rota- 
tion is a genetic trait it is probably polygenic. Many genes may be 
involved in determining the direction of rotation of the ootheca and 
a long period of intensive inbreeding may be required to show this. 
One difficulty lies in the fact that although one can select levorotatory 
females for breeding, the males have no comparable visible character 
to indicate what their genetic makeup is for this trait. 
SUMMARY 
All cockroaches extrude their eggs with the micropylar ends 
dorsally oriented and the keel of the ootheca facing upwards. Some 
species carry the ootheca in this position until depositing it, whereas 
others rotate the egg case 90° before dropping or retracting it into 
the uterus. The position in which the ootheca is carried at the time 
it is deposited is significant taxonomically and also played an im- 
portant role in the evolution of ovoviviparity and viviparity. 
Rotation occurs only in some members of the Blaberoidea (Poly- 
phagidae, Blattellidae, and Blaberidae — the phyletic line in which 
internal incubation evolved) but not in the Blattoidea (Crypto- 
cercidae and Blattidae — the line in which ovoviviparity did not 
evolve). Rotation reoriented the ootheca so that the long axes of the 
eggs lay in the plane of the cockroach’s width, a position which 
allowed for the stretching of the uterus once the egg case was 
retracted into the female’s body. Rotation in the oviparous Blat- 
tellidae may be considered to be a preadaptation for the evolution of 
internal incubation in the Blaberidae. 
The type of rotation found in the Polyphagidae is considered to 
be primitive because none of the eggs are hidden within the vestibu- 
lum ; the polyphagid ootheca has a flange by which it is held in the 
