Oöthecae of the Blattaria

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Abstract
The evolution of ovoviviparity and viviparity in the Blattaria necessitated a change from a hard rigid oötheca that was dropped shortly after its formation, to a soft, flexible, reduced egg case which was retracted internally into a uterus. Such changes have taken place in the oöthecae of the Blaberoidea (Polyphagidae, Blattellidae, Blaberidae), the phyletic line which evolved ovoviviparity, but not in the Blattoidea (Cryptocercidae, Blattidae). In the blaberoid line, polyphagid oothecae have keels and an anterior flange. Respiratory structures, denticles, and the production of calcium oxalate crystals (which undoubtedly contribute to the rigidity of the oötheca) arose within the polyphagids. The flange became markedly reduced in some Polyphagidae and was lost in most Blattellidae, although relics of this structure can still be seen in some Plectopterinae and Blattellinae oöthecae. In some Blattellidae (Plectopterinae, Blattellinae, Ectobiinae) there is a marked decrease in the size of the denticles and a tendency for the thickened margin of the keel to lie flat against the micropylar ends of the eggs. The oöthecae of most Blattellidae possess large amounts of calcium oxalate crystals. However, species of Blattella and Chorisia that retain their oöthecae externally during embryogenesis show a gradual loss of this compound. In the Blaberidae, all of which incubate their eggs internally, the keel, as it occurs in the blattellids, has been lost; in some blaberids greatly reduced keels are present as relics. The oöthecae of all blaberids are flexible, lack calcium oxalate crystals, and are thin compared to most oviparous species. The greatest reduction of the oöthecal membrane occurs in the viviparous species Diploptera punctata (Eschscholtz).

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