That particular careful reading is a reading that saves his rhetorical questions to the reader and discards his answers. Not very good scholarship.
One of the ocservations Darwin made was that the fossil record should be replete with evidence of transitional species, a record which simply does not exist.
In his defense, Darwin did not have the advantage of an understanding of DNA which we now possess. Those who persist in defense of this position are lately relying on "puntuated eqilibrium" to explain the movement from one form to another. Not very good scholarship.