1930's story: "The Brain Stealers of Mars" by John W. Campbell

Thanks to the industrious folks at the Internet Archive, you can read online or download “The Brain-Stealers of Mars” (1936), an adventurous novelette penned by influential science fiction editor John W. Campbell Jr. and illustrated by pulp artist Alex Schomburg, as it was reprinted in the 1952 issue of Wonder Story Annual magazine.

“Penton and Blake find Mars a pleasant place to be— 
until they run afoul of the thushol, which can imitate anything!”