One conceives of the counterpoise in Stock, of Male and Female complements, as being akin to that of the opposite and complementary curves of an arch. So long as equipoise is sustained by the perfect balance of the contrary curves, so long each re-inforces the other to support a heavy superstructure of development. Lopsidedness of either curve leads to collapse. VIII _Vigour is Male. Vitability is Female_ "Vigour," which breeders regard as a potent factor in heredity, is commonly confounded with Vital Power, or Vitability; although the two would seem to be diametrically opposite in cause, in nature and effect. An athlete, in so-called "condition," is in the prime of Vigour; his muscular and nervous powers being at high levels of structure and of functioning. His Vital powers are proportionally at low ebb, however; as is proved by his notable lack of recuperative power in illness. He is bad subject, indeed, in respect of progress and recovery from disease. Feeble-minded persons possess but little Vigour of brain or of body, yet their Vital power, as shown in healthy organic functioning and vitativeness, is often extraordinary. Vigour is an expression of nervous energy, and is generated by the brain. Vitability is Life-power, and results from vital organs efficient both in structure and in processes. It is engendered in the Reproductive System; which may be regarded as the power-house of Life and vital function. _Vigour_ is the power of Differentiation, or Individuation, of an organism, structural and functional, physical and mental, in terms of its relation to environment. _Vitability_ is the intensification of the individualism and of the functioning of an organism in terms of Life-power. Vigour, being katabolic, a male and a Dominant trait, manifests in man (as in plants) as Tallness, or the expenditure of vital energy upon the material plane, in growth and stature; as too in functional initiative and activity, both physical and mental, on the material plane. Vitability, being anabolic, a female and a Recessive trait, manifests as Dwarfness, or the conservation of vital energy upon the material plane, in respect of growth and stature; as too in weakness, or inhibition of vigour and activity, both physical and mental. The male trait of Vigour makes men larger, stronger, hardier, and more resistant to disease than women are. The female trait of Vitability makes women healthier, more charged with vital power and temperament, more recuperative from disease, and longer-lived than men. The complementary inherences of Vigour and Vitability, derived respectively from the two parents, and supplementing one another in offspring, endow him or her with fine form and structure, healthy vital organs and efficient function, power of Life and nervous energy.