A ‘Pickled Punk’ is a sideshow term for a preserved human fetus, usually deformed and usually displayed as a specimen in a jar or other vessel. 'Baby Show', 'unborn,' 'life,' 'bottle,' and 'freak baby' are other terms applied to this particular backend show.
The practice of preserving and displaying prodigious births is centuries old. In the 1600’s King Frederick III of Denmark had a personal collection of punks numbering in the thousands.The deformities present in pickled punks are incredibly varied.  
The classic pickled punk, floating in a jar of preserving fluid, became most popular during the golden age of sideshows during the 1930's  and experienced a great resurgence in the 1950’s and 1960’s. During that era many punks were linked to drug abuse, at least in the banner lines outside. Several sideshows featured extensive punk displays – some authentic and others gaffed (faked). Following this era, laws began to restrict the display of punks. To complicate matters, laws differed from state to state  making traveling displays almost impossible. The question of whether punks qualify as ‘human remains’ further complicates the laws. Today, because of legalities, none that I'm aware of exist on any midway. The best place to find pickled punks is in research or university laboratories or medical museums like the Mutter Museum in Philadelphia. The world’s largest collection of pickled punks, once owned by Peter the Great, is currently on display at the Kuntskammer Museum in St. Petersburg, Russia.
The great modern showman, Ward Hall, once had one of the largest punk shows in the United States. During one season he was fined due to the fact that the display of human remains was illegal in the state he had set up his show in. He replaced his punks with rubber replicas called ‘bouncers’ and continued his tour only to be fined again in another state for being a ‘conman’, displaying ‘fakes’ and ‘false advertising’.
Lou Dufour is known as the Father of the Unborn shows. In 1921, while playing a spot, he visited the Smithsonian Museum in washington D.C.where he saw people standing in line to view "human specimines". He never forgot the exhibit and several years later, in 1927 when playing a fair in Shreveport Louisiana, he spotted  a lineup of people waiting to enter a tent where Dr. Albert Jones was exhibiting a collection of twenty human specimens. He was a local doctor with a good practice and no desire to enter show business. After several days of persuasion, the  doctor sold him the collection. It was named the "Unborn" and opened with the Johnny J. Jones Shows in Largo, Fla., in early 1928.
Lou received an excited call from the Largo fair manager one morninig during the run. The quartet of Henry Ford, Thomas Edison, Harvey Firestone, and a Dr. Goodman, had come to see the "Unborn" Show. Lou opened the show and made the pitch for them. When they expressed approval and enthusiasm He knew he really had something.
Edison was deaf so Lou hollered into his old-fashioned horn that he held to his ear. Lou asked what impelled them to come so early in the day, and Edison explained, "Last night I had these gentlemen to my home as dinner guests and all my wife could talk about was your exhibit. We decided to see for ourselves and I'm glad we came". . .