Period of variability, relation of, to sexual selection.
Periodicity, vital, Dr. Laycock on.
Periods, lunar, followed by functions in man and animals.
Periods of life, inheritance at corresponding.
Perisoreus canadensis, young of.
Peritrichia, difference of colour in the sexes of a species of.
Periwinkle.
Pernis cristata.
Perrier, M., on sexual selection; on bees.
Perseverance, a characteristic of man.