In the middle of the first season, Jerry took about five weeks off before the break, most likely to come back to the states to be with his daughter, who suffered a debilitating illness. During this time, from episodes 11-15, Peter Friedman filled in as puppeteer (and you'll notice that none of Jerry's characters appeared and those that did didn't speak); he was also in a couple of episodes at the beginning of Season 3. Friedman, who later played Tateh in the original Broadway production of the Tony-winning musical "Ragtime", voiced the following Muppets:
Lead Ragg Mopp (#11 Lena Horne)
Various (#12 Peter Ustinov)
Pa, of the Gogolala Jubilee Jug-Band (#13 Bruce Forsyth; voice only)
Crocodile in "Never Smile at a Crocodile" (#14 Sandy Duncan)
#15 Andre the Artist in "Look at that Face" (#15 Candice Bergen)
Various (#50 Leo Sayer)
Lead Singing Fireman in UK Spot, "I Don't Want to Set the World on Fire" (#51, Roy Clark)
7-foot tall talking carrot, Pirates of Penzance medley w/Gilda Radner (#52)
Various (#53 Pearl Bailey)
Hope this helps!
David "Gorgon Heap" Ebersole