What's the meaning of " I don't mean .....?" in this sentence?
A man did a lot of experiments with monkeys and used radiation on their unborn babies. Some very strange monkeys were born, but there were two who were telepathic.

" Monkeys", Harl said, "They are one thing. People are another.".
""Do you think that Drewitt didn't know that? One of the scientists in his group was called Whittaker...."
"Arthur Wittaker? I was at school with him."
"Yes, well, his wife also worked with the group , and she wanted to try......"
"You don't mean ......?" Harl shook his head in surprise.
"Surely not!"

This is from a science fiction novel. What's the meaning of " You don't mean .....?" in this sentence?

I mistook this title. " You don't mean .....?" is correct.

Question

What's the meaning of " I don't mean .....?" in this sentence?
A man did a lot of experiments with monkeys and used radiation on their unborn babies. Some very strange monkeys were born, but there were two who were telepathic.

" Monkeys", Harl said, "They are one thing. People are another.".
""Do you think that Drewitt didn't know that? One of the scientists in his group  was called Whittaker...." 
"Arthur Wittaker? I was at school with him."
"Yes, well, his wife also worked with the group , and she wanted to try......"
"You don't mean ......?" Harl shook his head in surprise.
"Surely not!"

This is from a science fiction novel. What's the meaning of " You don't mean .....?" in this sentence?

I mistook this title. " You don't mean .....?"  is correct.

Answer

"You don't mean..." is the guy's way of asking "are you saying [that]..." They didn't complete the rest of the sentence because the other person understood what he was asking and replied. If he had completed it might have been something like "you don't mean...the wife was etc. etc.?" Hope this clarifies!

Answer

The "You don't mean..." is something that is intentionally left hanging (the "...") or incomplete because it leaves the listener/audience to imagine the unthinkable thing that is not being said.

In this case, since they're talking about radiation experiments on unborn baby monkeys, and the Whittakers are both scientists, married, and working on the same project, it would lead people to imagine that they had performed (or were thinking about performing) the same radiation experiment on their own unborn child(ren).

Answer

Hi!

The expression 'you mean that'  is the same as saying ' what you (really) want to tell me is that...'. In your sentence, it seems as if the person saying 'you don't mean' wants to ask 'you are not trying to tell me she wanted to try, aren't you?'. It's more to show emphasis that he can't believe the woman would be capable of trying such thing.

I hope it helps!