Here are some scraps from the Ingeborg Willy Scrapbook (who worked in the Pen and Ink Department in the late 1930's).
What I liked about the Cactus was the fact that you can see the erasure marks as the character was refined. It really gives you insight into the artist's process.
I was just looking at these and thought that the Disney donkey sure looked a lot like Sparky from the Fleischer "Sparky and Hunky" series....
Ingeborg Willy Scraps
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From "Don Donald" (1937). From the Ingeborg Willy Scrapbook.
Wikipedia: Don Donald (first released on January 9, 1937).was Donald Duck's first headliner cartoon. It introduces Donna Duck for the first time as Donald's girlfriend. Clarence Nash voices both since Donna's voice is the same as Donald's an octave higher. The cartoon takes place in Mexico and tells the story of Don Donald going to greet his girlfriend Donna. Donald rides a burro and lets Donna also ride it, but unfortunately Donna hates the animal. Angered at blowing his chances with Donna, Donald trades in his burro for a flashy new red car. Donna loves the new car until it breaks down in the middle of nowhere. She leaves Donald, who is left with nothing but a shrunken sombrero.