Epigraphs are like little appetizers to the great entrée of a story. They illuminate important aspects of the story, and they get us headed in the right direction.
"You are saved," cried Captain Delano, more and more astonished and pained; "you are saved: what has cast such a shadow upon you?"
Herman Melville, Benito Cereno
Harry: I tell you, it is not me you are looking at,
Not me you are grinning at, not me your confidential looks
Incriminate, but that other person, if person,
You thought I was: let your necrophily
Feed upon that carcase…
T.S. Eliot, "The Family Reunion"
With the way that quotation from Benito Cereno ends, we might think Captain Delano is asking a rhetorical question—or maybe he's appearing on Jeopardy!.
But if we thumb to the end of Melville's short novel (or just hit "find" on ye olde computer), we learn that Benito Cereno, a Spanish captain whom Delano has just rescued from a slave insurrection, replies pretty directly: "The N***o," he says.
Why would Ellison leave that part out? Did he get up for tea and just forget to finish the sentence? Or is he trying to say something about the way that African Americans can become invisible and yet still cast the long shadows that trouble Benito after Delano rescues him? Lots to chew on, that's for sure.
As for the excerpt from the Eliot verse play, we should get some terms straight first. To start with, necrophily is synonymous with necrophilia, or the terrible affliction some people have when they're obsessed with corpses, often in a sexual way. ("Carcase" is just a fun British way of saying carcass.)
To make matters clear, Invisible Man is definitely not about sex with dead carcasses. Nor is the Eliot play. In the play, Harry argues that the people looking at him aren't really seeing him, and he gets so angry about this that he compares their vision of his identity to necrophilia—what they see when they look at him, what they're so obsessed with, isn't a real human being at all, but a carcass. As such, the people looking at him are necrophiliacs.
The narrator of Invisible Man faces a problem similar to Harry's. No one sees him properly. Does this mean Mr. Norton, Dr. Bledsoe, Brother Jack, Ras the Exhorter, etc. are basically trying to feed off the narrator's carcass? We'll leave the answer up to you.