The real answer is that nobody played bass on it - Jaco deliberately wanted to get away from the "bass virtuoso" thing and so didn't put down any bass on the tapes.
The master tapes were sold on to a Japanese businessman, who saw it as investment - but then realised that the big selling point for any Jaco record was the bass - so bass was added secretly by an anonymous session guy and then it was kept quiet in the hope the album would sell and nobody would ask where the virtuoso bass stuff was|!!
There's a load of stuff about this in the Milkowski book and across the net!
