He begins with Ignatius, concerning some Heretics, (Ignatius' Epistle to the Smyrneans) that received not Eucharist or Oblations, because they confess not the Eucharist to be the Flesh of Christ. (T. B. Section 1)(Part 1, "An Answer to Some Testimonies produced by T. B. from the Fathers of the Six First Centuries, for Transubstantiation," pp. 49-50 - spellings modernized)
The Heretics he means, were the Followers of Simon and Menander, who denied the reality of Christ's Flesh, and for that Reason admitted not the Eucharist. And what is this to Transubstantiation, that some Heretics, because they did not believe that Christ was really Incarnate, would not admit the Eucharist, the Symbols whereof represented and supposed a real Incarnation? Heresy is prolific of Heresy, and their Disbelief of the Incarnation made them reject the Eucharist, lest they would be forced to confess the Flesh of Christ. For if they allowed the Symbols of a true Body, they would be obliged to grant a true Body, since a mere Phantom can have no Sign or Symbol. Thus your Cardinal Bellarmine answers for us (Bellarmine On the Eucharist, book 1, chapter 1, p. 400), Lest the Calvinists (says he) should Glory of the Antiquity of their Opinion, it is to be observed, that those ancient Heretics did not so much oppose the Eucharist as the Mystery of the Incarnation. For therefore (as Ignatius shows in the same place) they denied the Eucharist to be the Flesh of the Lord, because they denied the Lord to have Flesh. If then in the Judgment of your Cardinal these Heretics were no Calvinists, Ignatius in condemning them, neither condemns Calvinists, nor countenances Transubstantiators: What we teach, that the Elements are Sacramental Signs of Christ's Body, is as inconsistent with the Sentiments of those Heretics as Transubstantiation, since such Figures of a Body (as Tertullian argues against the Marcionites) prove the Reality of Christ's Flesh, and that it was no Phantom, which can have no Figure. I may add, That Theodoret, out of whose third Dialogue this Passage of Ignatius is restored (which was not to be found in former Editions of Ignatius) hath plainly declared against the Eutychians (as I have formerly observed) that the Symbols after Consecration recede not from their own Nature, but remain in their former Substance. And he must have a very mean Opinion of Theodoret's Judgment, who can think he imagined this Passage of Ignatius inconsistent with his own Opinion; which would have been to have helped the Heretics instead of confuting them. To conclude, examine this Testimony by the latter part of my fifth Rule, and show us where Ignatius says a Word of the changing of the Substance of the Bread into the Substance of Christ's Body: Which is the Doctrine of the Trent Council, and what T. B. was to prove.
Theodoret's Dialogue 3 "The Impasible" (mentioned by Bellarmine)
I should caution that I believe Bellarmine may, on some other occasion, have attempted to use Ignatius against a symbolic understanding of the Eucharist. In any event, however, Bellarmine (as alleged by Newcome) is correct in stating that the objection of the heretics to the Eucharist was a denial of Christ's true humanity - not a denial of a change of the elements.