The 'reasons' are not recondite; for fifteen MSS., at the least, have this arrangement.
Tyrwhitt is quite right; he is alluding to the true Shipman's Prologue; B 1163-90.
Only a few hours after writing this sentence, I found that Mr. Keightley, in his Tales and Popular Fictions, published in 1834, at p. 76, distinctly derives Chaucer's Tale from the travels of Marco Polo. I let the sentence stand, however, as an example of undesigned coincidence.
So in Mr. Hazlitt's edition; Warton originally wrote—'to believe this story to be one of the many fables which the Arabians imported into Europe.'
'All things can be known by Perspective, because all operations of things take place according to the multiplication of forms and forces, by means of this world's agents, upon yielding materials.'—Opus Minus (see Warton).