What fantasies did Dr. Manette have while in prison in Chapter 17 of A Tale of Two Cities by Charles Dickens?

On the night before she is to be married, Lucie sits with
her father under the plane-tree at their house in Soho.  Without knowing Darnay's
history, Lucie speaks to her father in the hopes that they will not be parted.  Her
father reassures her that his future will be all the brighter through her marriage. 
Further, he tells his daughter that her life should not be wasted for his sake.  Then,
he reminisces about how lonely he was in prison and how he looked at the same moon above
them now. 

“I
have looked at her, speculating thousands of times upon the unborn child from whom I had
been rent. Whether it was alive. Whether it had been born alive, or the poor mother’s
shock had killed it. Whether it was a son who would some day avenge his father. (There
was a time in my imprisonment when my desire for vengeance was
unbearable.)

Dr. Manette
thought about his unborn child from whom he had been taken, and he wonders if the mother
miscarried the baby from the terrible shock of losing her husband.  Or, he wonders, if
the baby lives, if it is female or male, a son who would avenge his
imprisonment. 

On evenings that he counted the
perpendicular lines he could draw upon the face of the moon, the prisoner of North Tower
wondered if he had a daughter who knew nothing of him.  As time passed, he wondered,
too, if she were married to a man who knew nothing of his fate. But, he had also
imagined his child coming to him at the prison and leading him out to
freedom.

Then, the doctor of Beauvais tells Lucie of a
phantom that he saw; this was another image that stood before him, one that moved,
unlike the figure on the moon.  It, too, resembled the mother. In the moonlight, he
imagined this phantom taking him out to show him her home that was full of loving
remembrance of her "lost father." She had his picture in her room, "and in her
prayers."  Her life was "active, cheerful"; but his "poor history pervaded it."  This
phantom showed the physician her children, who had been taught to pity him.  Whenever
they passed a prison, they looked up at the bars, whispering to each other.  And,
although the phantom came many times, she could not deliver him from his prison for more
than the little visits.

Then, Dr. Manette embraces Lucie
and tells her that even in his wildest thoughts, he was never as happy as he is now to
have known her and to be with her.