Sentence:  We may learn, to be sure, plenty of lessons from Shakespeare. We are not likely to have kingdoms to divide, crowns foretold us by weird sisters, a father's death to avenge, or to kill our wives from jealously ; but Lear may teach us to draw the line more clearly between a wise generosity and a loose-handed weakness of giving ; Macbeth, how one sin involves another, and forever another, by a fatal <WSD>parthenogenesis</WSD>, and that the key which unlocks forbidden doors to our will or passion leaves a stain on the hand, that may not be so dark as blood, but that will not out ; Hamlet, that all the noblest gifts of person, temperament, and mind slip like sand through the grasp of an infirm purpose ; Othello, that the perpetual silt of some one weakness, the eddies of a suspicious temper depositing their one impalpable layer after another, may build up a shoal on which an heroic life and an otherwise magnanimous nature may bilge and go to pieces. 
Meaning of the word marked with <WSD> tags:  "figurative uses of the biological senses"