Marcolina is not really a woman.

She is a she-professor, a she-philosopher, one of the wonders of the world perhaps--but not a woman." Yet even as he mused, he knew he was merely attempting to deceive himself, console himself, save himself; and all his endeavors were vain.
Olivo, who had now come up, addressed Marcolina.

"Have I not done well to invite some one here with whom you can converse as learnedly as with your professors at Bologna ?" "Indeed, Uncle," answered Marcolina, "there was not one of them who would have ventured to challenge Voltaire to a duel!" "What, Voltaire?
The Chevalier has called him out ?" cried Olivo, misunderstanding the jest.
"Your witty niece, Olivo, refers to the polemic on which I have been at work for the last few days, the pastime of leisure hours.

I used to have weightier occupations." Marcolina, ignoring this remark, said: "You will find it pleasantly cool now for your walk.

Goodbye for the present." She nodded a farewell, and moved briskly across the greensward to the house.
Casanova, repressing an impulse to follow her with his eyes, enquired: "Is Signora Amalia coming with us ?" "No, Chevalier," answered Olivo.