1967] 
Roth — Rotation of the Ootheca 
97 
making the counts the terminal eggs (those laid first and last) were 
not included since these are placed about on the midline and each 
lies partly on the left and right sides. Ten of the 20 oothecae had an 
even number of eggs on each side. Of the remaining io oothecae, 
9 had one more egg on the left side, and i had one more egg on the 
right side. These results contradict Brown’s hypothesis and it is 
likely that the direction of rotation is not influenced by the number 
of eggs on either side of the ootheca. 
Table 2. — Individual oviposition records of females of 
Ischnoptera rufa rufa showing the direction 
of rotation of their oothecae. 
Female 
Number 
Number 
Left 
of Oothecae Rotated to: 
Right 
l 
6 
0 
2 
4 
0 
3 
2 
0 
4 
2 
0 
5 
4 
1 
6 
3 
4 
7 
2 
5 
8 
2 
5 
9 
2 
3 
10 
1 
5 
11 
1 
4 
12 
0 
5 
13 
0 
6 
14 
0 
7 
15 
0 
7 
All of the females of Blattella germanica in our culture rotate 
their oothecae in one direction only, usually to the right. Although 
I recorded only one left-rotating female in Table i, I have observed 
several others and none rotated their oothecae in both directions. In 
rare cases the ootheca is carried with the keel dorsad, or the ootheca 
is incompletely rotated and is only slightly tilted to one side 
(Wheeler, 1889; Ross, 1929; Willis et al 1958). It seems logical 
that the direction of rotation is a genetic character and by inbreeding 
I have tried to obtain a strain of Blattella germanica in which the 
left rotating females occur more frequently. Initially, I reared 206 
female offspring from dextrorotatory mothers. Only one of the off- 
spring rotated to the left and the remaining 205 were dextrorotatory 
like their mothers. The one left-rotating female oviposited 4 times 
and all her oothecae were rotated to the left. The offspring of each 
