Otocysts, of Elasipoda, [571];
of Synaptida, [576]
Outer perihaemal ring, of Asterias rubens, [448];
development of, in Asterina gibbosa, [612];
represented by lantern-coelom of Echinus esculentus, [524];
by buccal sinus of Holothuria nigra, [566]
Ovary of gnat infected by Trypanosoma germs, [120]
Ovoid gland of Ophiothrix fragilis, [489]
Ovum of Sea-urchin, [7];
of Sarcocystis tenella, [108] n.;