I'm looking for the title of a paperback from the 50's or 60's. In it human sex has been replaced with a living organ attached to the penis. When aroused it functions as a vagina. Possibly to control population growth.
I think this might be Theodore Sturgeon's 1960 novel Venus Plus X.
from the Wikipedia entry:
Charlie Johns has been snatched from his home on 61 North 34th Street and delivered to the strange future world of Ledom. Here, violence is a vague and improbable notion. Technology has triumphed over hunger, overpopulation, pollution, even time and space. But there is a change Charlie finds even more shocking: gender is a thing of the past. Venus Plus X is Theodore Sturgeon's brilliant evocation of a civilization for whom tensions between male and female and the human preoccupation with sex no longer exist.
As Charlie Johns explores Ledom and its people, he finds that the human precepts he holds dear are profane in this new world. But has Charlie learned all there is to know about this advanced society? And why are the Ledom so intent on gaining Charlie's approval? Unsettling, compelling, and no less than visionary, here is science fiction at its boldest: a novel whose wisdom and lyricism make it one of the most original and insightful speculations on gender ever produced.
Here's the most descriptive scene:
The room was now totally dark, and the charts blazed with light In full color, they were the front and side views of a Ledom, clad only in the silky sporran which began perhaps an inch under the navel and fell, widening from perhaps a palm’s breadth at the top, to its lower edge, which was roughly three inches above mid-thigh, and which extended from die front of one leg to the front of the other. Charlie had seen them, already, longer and shorter than this, and also red, green, blue, purple and snowy white, but he had yet to see the Ledom who went without one. It was obviously a tight taboo, and he did not comment.
“We shall dissect,” said Mielwis, and by means unperceived by Charlie Johns, he caused the chart to change: blip! And the sporran, as well as the superficial skin under it, were gone, exposing the fascia and some of the muscle fibres of the abdominal wall. With a long black pointer he magically produced, he indicated the organs and functions he described. The tip of the pointer was a needle, a circle, an arrow and a sort of half-parenthesis at his will, and his language was concise and ultimately geared to Charlie’s questions.
The anatomical details were fascinating, as such things so often are, and for the usual reason which overwhelms anyone with the vestiges of a sense of wonder: the ingenuity, the invention, the efficient complexity of a living thing.
First of all, the Ledom clearly possessed both sexes, in an active form. First of all, the intromittent organ was rooted far back in what might be called, in homo sap., the vaginal fossa. The base of the organ had, on each side of it, an os uteri, opening to the two cervixes, for the Ledom had two uteri and always gave birth to fraternal twins. On erection the phallus descended and emerged; when flaccid it was completely enclosed, and it, in turn, contained the urethra. Coupling was mutual—indeed, it would be virtually impossible any other way. The testicles were neither internal nor external, but superficial, lying in the groin just under the skin. And throughout, there was the most marvelous reorganization of the nervous plexi, at least two new sets of sphincter muscles, and an elaborate redistribution of such functions as those of Bartholin’s and Cowper’s glands.
When he was quite, quite satisfied that he had the answers, and when he could think of no more, and when Mielwis had exhausted his own promptings, Mielwis flicked the two charts with the back of his hand and they slid up and disappeared into their slots, while the lights came up.
Charlie sat quietly for a moment. He had a vision of Laura—of all women … of all men. Biology, he remembered irrelevantly; they used to use the astronomical symbols for Mars and Venus for male and female… . What in hell would they use for these? Mars plus y? Venus plus x? Saturn turned upside down? Then he heeled his eyes and looked up at Mielwis, blinking. “How in the name of all that’s holy did humanity get that churned up?”
Late in the book Charlie learns that the Ledom were the product of surgical grafting rather than mutation:
“What changed you, Charlie Johns? You thought very well of us a few hours ago. What changed you?”
“Only the truth.”
“That there is no mutation.”
“Our doing it ourselves makes that much difference? Why is what we have done worse to you than a genetic accident?”
“Just because you do it.” Charlie heaved a deep breath, and almost spit as he said, “Philos told me how old a people you are. Why is what you do evil? Men marrying men. Incest, perversion, there isn’t anything rotten you don’t do.”
“Do you think,” said Mielwis courteously, “that your attitude is unusual, or would be if the bulk of mankind had your information?”
“About a hundred and two percent unanimous,” Charlie growled.
“Yet a mutation would have made us innocent.”
“A mutation would have been natural. Can you say that about yourself?”
You may be thinking of the 1965 short story "Coming-of-Age Day" by A. K. Jorgensson, originally published in Science Fantasy, September 1965, available at the Internet Archive. You might have read it in the 1965 paperback anthology 11th Annual Edition: The Year's Best S-F edited by Judith Merril, or the 1969 paperback anthology Dark Stars edited by Robert Silverberg.
The appliance is called a "consex", available in both sexes, for men and for women. The narrator is a boy who is being fitted with one:
"Ready to have a consex fitted! Now, Andrews, this is a most private matter which I think will explain itself. We are not afraid to be scientific about sex as a subject, but I trust you will keep this to yourself. If you are not completely satisfied—for any reason, whatsoever—tell no one but come and see me. Is that understood?"
"I am a sexiatrist, actually, not a doctor. Now come and look in this glass container."
I looked. As I believe it usually does to others, it struck me with a sort of horror to see this thing alive, a collapsed sort of dumpling with ordinary human skin, sitting in its case like a part of a corpse that had been cut off.
"Get used to it," he said. "It's only ordinary flesh. It has a tiny pulse with a primitive sort of heart, and blood, and muscle. And fat. It's just flesh. Alive, of course, but perfectly harmless."
[. . . .]
"It's yours," he announced.
I nearly fainted with horror. It strikes everyone that way until they realize how simple, harmless and useful free living tissue can be, and its many healing properties. It embarrassed me to guess where the "consex" was to be located on my body, and my intuition was uncertain with equally embarrassing ignorance. But one only has to wear a consex a short while to realize how utterly natural it is, and how delightfully pleasant when in active use. It is a boon to lone explorers, astronauts, occupants of remote weather and defense stations, and so on.
[. . . .]
I feared to do anything. He said, "I'll show you how it works. Don't take it off for at least a week, not for any reason. See me at once if there is any discomfort. Later on, you may remove it for athletics, though you can do most things with it on—swimming, for instance. In the toilet it rolls up easily enough. But don't disturb the suction or play around. It clings well if you leave it alone, and it's very comfortable."
He took me into a private cubicle, where I undressed and lay under a soft blanket. Then he brought the thing in on his hand and pulled the blanket back.
I held my breath. It was the worst moment of my life for fear, though not for pain.
"I've stimulated it a bit," he said. "It'll take over for you this time, but every time after that it's up to you to make the first move, or nothing will happen. It's very responsive. Now you must lie here half an hour until I let you go."
He let it rest between my thighs, and it covered all those parts you never see on pictures of nudes except those in classical religious paintings. It was comfortable. It felt pleasant. This first time when the sexiatrist goes out and leaves one alone with one's body and one's consex and one's private thoughts is the crucial one.
The narrator overhears a sexiatrist in another room arguing with a religious objector:
"I see. You don't believe that this country is heavily overpopulated? You don't believe that before consexes came out the years of adolescence were years of miserable misfits trying to adjust to a half-baked situation? And that boys slept promiscuously in spurious natural sexual relations, that girls had illegitimate babies sometimes from the earliest years it is possible to conceive, and that mere children contracted serious venereal diseases from these methods.
"You think you can do without all this. And what sort of substitute will you have? Tearing about on a rocket-scooter or getting drunk! Raping a woman or just stealing her handbag! And if and when you grow up . . .
"Did you know that there are ten million bachelors and the same number of spinsters in this country who have never been married nor had a so-called love affair but are sexually wholly satisfied and consummated? Did you?"
[. . . .]
"I am an authority on this, lad. You mean to say you still haven't accepted that the government knows what is best for the nation after all I've told you?"
[. . . .]
"I'll give you one more chance," said the sexiatrist. "In case you're ashamed or anything. Nurse, tell me, do you wear a consex?"
"Yes, doctor, I do."
"A male consex?"
"And you like it? It's comfortable, not unhealthy? You can do what you like? You don't feel guilty about it?"
"I love it," she said. "I've never had difficulty with it. It always responds to my lead and never disobeys."
"Thank you. Now, boy, are you satisfied?"