of Caenomorpha uniserialis, [155];

of Vorticella, [156], [157]

Unequal fission in Spirochona, [147]

Upper arm-plate, of Ophiuroidea, [491];

of Ophioteresis, [491];

absent in Cladophiurae, [491], [500]

Urechinidae, [554] n.

Urine, [13]

Urocentrum, [137], [141] n.

Uronema, [137], [141] n.