Yeah that's the notorious Hollywood Palace "For What It's Worth/Mr. Soul" medley.
"The band moved back and forth between recording sessions and live appearances on both coasts. A number of different bassists were used, such as Mike Barnes and Jim Fielder of The Mothers of Invention. In one instance – a live performance on the television show Hollywood Palace – Springfield's road manager, who couldn't play bass, held a bass with his back to the camera while the band mimed to a prerecorded track"
Why the bassist round-robins?
"In January 1967, the group took an advance from the record company and flew to New York to perform at Ondine's, a club where The Doors would also play. It was at this time that Palmer was first arrested for possession of marijuana and summarily deported back to Canada."