Oudemans on Thysanura, [182]

Oustalet on Odonata, [422], [423]

Outer margin of wing, [108]

Ovaries, [137], [138];

of earwigs, [211];

of Oedipoda, [283], [284];

of Perla, [404];

of Thysanura, [188]

Oviduct, [139], [392]

Oviposition, [229], [246], [265], [290], [291], [440];