Odontonectes, [660]

Odontostomus, [611], [613]

Oenoscopus, [545]

Oesophageo-cutaneous duct, [281]

Oikoplasts, [65]

Oikopleura, [68], [67], [69];

transverse section, [67];

longitudinal section, [68];

O. cophocerca, [66];

O. dioica, [70];