"Embryo" is a classic Pink Floyd tune that never appeared on any of their original albums, although it did show up later on the mini-compilation Works.
It was part of their live set from 1968 to 1972. I want to say it was last performed on the DSOTM tour and then permanently dropped thereafter.
What an awesome find...the band performs it live here. This is the belly of the beast; Pink Floyd in all their awe-inspiring mystery and creativity...long before there was MTV.
Radiohead fans, take note...these are the Jedi Masters of art rock that gave Yorke and Greenwood some of their ideas for what you get from them these days.