PSYCHE 
Vol. 74 
June, 1967 
No. 2 
THE EVOLUTIONARY SIGNIFICANCE OF ROTATION 
OF THE OOTHECA IN THE BL ATTAR I A 
By Louis M. Roth 
Pioneering Research Division 
U.S. Army Natick Laboratories, Natick ? Mass. 
The newly-formed ootheca of all cockroaches projects from the 
female in a vertical position, with the keel and micropylar ends of 
the eggs dorsally oriented. All of the Blattoidea (Fig. 1) and some 
of the Blaberoidea carry the egg case without changing this position. 
However, in some of the Polyphagidae (Figs. 11-16) and Blattellidae 
(Figs. 2,3), and all of the Blaberidae, the female rotates the ootheca 
90° so that the keel faces laterally at the time it is deposited on a 
substrate (Polyphagidae, Blattellidae), carried for the entire embryo- 
genetic period ( Blattella spp.), or retracted into the uterus (all 
Blaberidae). According to McKittrick (1964), rotation of the 
ootheca frees the keel from the valve bases which block an anterior 
movement of the ootheca while it is in a vertical position, and it 
orients the ootheca so that its height lies in the plane of the cock- 
roach’s width, thus making it possible to move the egg case anteriorly 
beyond the valve. It is likely that by the time the ootheca had evolved 
to the stage where it was retracted internally, the height of the keel 
had been greatly reduced (e.g., in Blattella spp.) and it would not 
be necessary to free its keel from the valve bases. The eggs of 
Blaberidae increase greatly in size in the uterus during embryogenesis 
(Roth and Willis, 1955a, 1955b). A logical advantage for rotating 
the ootheca prior to retraction resulted in orienting the eggs in the 
female’s body in a position which would permit the uterus to increase 
in size as the embryos developed. When stretched by a newly de- 
posited ootheca, the uterus of a blaberid presses against the inner 
surfaces of the tergum and sternum but there is lateral room for 
expansion. If the ootheca was not rotated prior to retraction, the 
long axes of the eggs would lie vertically and during gestation the 
uterus would have to stretch dorso-ventrally, a direction which allows 
little room for expansion in these relatively flat insects. 
Manuscript received by the editor December 15, 1966 
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