Did he perceive that his auditors, propped up in their cells, had gradually fallen asleep during his entomological lecture?
No; certainly not.

He lectured for himself.

Dick Sand no longer questioned him, and remained motionless, although he did not sleep.

As for Hercules, he had resisted longer than the others; but fatigue soon finished by shutting his eyes, and, with his eyes, his ears.
For some time longer Cousin Benedict continued to lecture.

However, sleep finally got the best of him, and he mounted to the upper cavity of the cone, in which he had chosen his domicile.
Deep silence fell on the interior of the cone, while the storm filled space with noise and fire.