John W Campbell, Jr's "The Brain Stealers of Mars" (novelette, puzzle, free): Precursor to "Who Goes There?" & "Mars is Heaven"

I know of at least two very famous stories directly descended from it: Campbell's own "Who Goes There?" (download) & Bradbury's "Mars is Heaven" (download MP3). Plus any number of less well known ones, among them Eric Frank Russell's "Mesmerica", Philip K Dick's "The Father-Thing" (read online), & Fredric Brown's "Nothing Sirius" (download as part of a larger package).

Telling style is very pulp-era, but it's not a bad read & an important classic.

Story summary.

Rod Blake & Ted Penton ran away to Mars, after adventures on moon & Venus, when human authorities got hot on them for doing some banned experiments with atomics. So far, they are the only humans capable of interplanetary flight.

They will meet two kinds of natives on Mars: "thushols" & "centaurs".

1. Thushols are parasites capable of both shape shifting & reading your mind.
2. Centaurs are local intelligent beings that once had a technological civilization that now lies in ruins. Because they've lost the urge. Because thushols now comprise 31% of centaur population, indistinguishable from normal centaurs. They kill centaur babies & implant themselves in their place - always maintaining the magic ratio. Centaurs cannot kill even the ones they suspect, because, if they're wrong, they'll be killing their own!

Thushols had once visited earth, as centaurs' parasites, when centaurs tried to establish colonies there. That was hundreds of years back, & it didn't work out. But that's the source of centaur legends on earth.

Now that Man has advanced to space travel, thushols have decided he would make a worthy host. So they've put impostors among the two human visitors - there are now 13 Blakes & 12 Pentons! How will the originals distinguish from the fake ones, & ensure not only that thushols don't reach earth but warn the earthmen of danger?

Notes.

1. "Campbell's interest in the idea of a shape-changing alien can be traced to his early childhood, when his mother and her identical twin frequently put on each other's clothes in order to play a trick on him. "
2. 'The "Penton and Blake" series impressed a young Isaac Asimov so much that he started his own "Powell and Donovan" stories about two robot-snafu troubleshooters'.
3. It appears to be a curious feature of many old stories - physical travel is possible to far away places, but not electronic communications!
4. Another rather common feature of old stories: advanced animal telepaths inhabit Mars, but Venus is a jungle world of "ferocious plants".

Fact sheet.

First published: Thrilling Wonder Stories, December 1936.
Read full text at Scribd.
Rating: A.
According to ISFDB, this story is the first in a series of 6.

Related.

1. Stories authored/edited by John Campbell.
2. Stories about Mars or its moons.
3. Tuesday Classics.
4. Fiction from 1930s.