Proctotretus tenuis, sexual difference in the colour of.
Profligacy.
Progenitors, early, of man.
Progress, not the normal rule in human society; elements of.
Prong-horn antelope, horns of.
Proportions, difference of, in distinct races.
Protective colouring in butterflies; in lizards; in birds; in mammals.
Protective nature of the dull colouring of female Lepidoptera.
Protective resemblances in fishes.
Protozoa, absence of secondary sexual characters in.