The reference is to the celebrated Eth. Nic. X, iv, 8: "Pleasure makes activity perfect, not as a habit of skill perfects the skilful act, but as a sort of efflorescence marking completeness, as bloom perfects maturity," or as we might say, like the bloom on ripe grapes or peaches. So Professor Stewart (Notes on Nicomachean Ethics, ii, 418) speaks of "the law of our nature, that function is primary and pleasure only attendant," -- which is the real refutation of this objection and of hedonism in all its forms.
Of God and His Creatures: 3.26