unequal length of life in two sexes of, [58];
parthenogenesis of, [294].
Pieris napi, length of life of, [44].
Pig, length of life of, [6].
Pigeon, length of life of, [36];
cross-breeding of, [332].
Pike, length of life of, [6].
Pisidium, length of life of, [56].
Planorbis, length of life of, [56].