——, habit of laying eggs together, [218].
——, American, two species of, [349].
Otter, habits of, how acquired, [179].
Ouzel, water, [185].
Owen, Prof., on birds not flying, [134].
——, on vegetative repetition, [149].
——, on variable length of arms in ourang-outang, [150].
——, on the swim-bladder of fishes, [191].
——, on electric organs, [192].
——, on fossil horse of La Plata, [319].