Oesophageal "bone," [391]
Oesophageal nervous ring, [118], [121]
Oesophagus, [114], [124], [403]
Oestropsides, [482]
Oligonephria, [175]
Oligoneuria garumnica, nymph, [434]
Oligotoma michaeli, [351], [354];
O. saundersi, [352];
O. insularis, [354]
Ommatidium, [98]