[PD] Couldn't creat [gemlist]. Also, how to destroy objects?

[Dudley Brooks]

Pd-0.39.3-extended, MacBook Pro OSX 10.4

I downloaded /Gem/examples/advanced/19.pointer.pd and 
...../20.double-gemhead_vs_repeat.pd, to learn how to create multiple 
instances of objects.  They both have some subpatches that use 
[gemlist].  I got the error "gemlist ... couldn't create".

Those two patches were not in 0.39.3-extended.  Are they and [gemlist] 
itself part of a more recent version, or what?

Also, a dumb question:  How to create (at various times) and destroy (at 
various times) geos, abstractions, etc.?  That is, how to have various 
things pop in and out of existence (in the Gem window, at least) as the 
"performance" runs?

Thanks.

-- Dudley