"Egg and Ashes" (If, November 1960) -- Brief tale of an alien organism which can disguise itself in many forms, eventually becoming part of a human being's nervous system. It all leads up to a variation on an old myth.
BODY SNATCHERS?
"A-W-F Unlimited" (Galaxy, June 1961) -- Satiric comedy about an advertising agency hired to find out why not enough women are volunteering for the Space Force. Too silly for my taste.
"Mating Call" (Galaxy, October 1961) -- Humans investigate an alien species that somehow uses music during their reproductive cycle, with unexpected results. An interesting notion, but the last line leads to a really dumb twist.
"Try to Remember" (Amazing, October 1961) -- A giant alien ship lands on Earth and humanity is given the choice of communicating proerly or being destroyed. A pretty good story which gets a bit mystical at the end.
"Mindfield" (Amazing, March 1962) -- On a far future Earth where the populace has been psychologically conditioned against any form of aggression, a man from the old days is revived. An interesting, complex story.
DEMOLITION MAN?
"The Tactful Saboteur" (Galaxy, October 1964) -- Another adventure of the "saboteur extraordinary" Jorj McKie. Here he has to find out what happened to another saboteur who happens to be a member of a species in which each "individual" has multiple bodies, but only one of them has self-awareness. Not bad.
"Mary Celeste Move" (Analog, October 1964) -- Short, darkly satiric tale of a near future where everything and everybody moves at a very rapid pace, and why people are suddenly moving from some parts of the USA to another for seemingly no reason. A good story.
"Greenslaves" (Amazing, March 1965) -- In a future Brazil which is eliminating insects in order to promote agriculture, insects evolve to form a group mind which can take the form of humans. Later expanded into the novel The Green Brain. A good ecological fable.
MIMIC?
"Committee of the Whole" (Galaxy, April 1965) -- The US Congress has to consider the implications of an invention which gives every individual enormous power, for peaceful or harmful purposes. A thoughtful, brief tale.
"The GM Effect" (Analog, June 1965) -- A medical experiment accidentally gives people the ability to remember the lives of their ancestors in great detail, changing the commonly accepted view of history. A pessimistic, downbeat story.
"The Primitives" (Galaxy, April 1966) -- Pretty goofy yarn about a guy who steals a gigantic Martian diamond from a Russian sub, and how a time machine brings back a prehistoric woman (with four breasts) who has the skill to cut it properly. Nutty stuff.
"Escape Felicity" (Analog, June 1966) -- An explorer of deep space who has been psychologically programmed to return home encounters aliens on a distant world. Interesting, with an ironic ending.
"By the Book" (Analog, August 1966) -- Engineering story about a guy who has to go inside one of the giant tubes that allow instant interstellar travel and find out what's wrong with it. OK for that sort of thing.
"The Featherbedders" (Analog, August 1967) -- Aliens in human form investigate the dictatorial sheriff of a small town who seems to be one of their own kind. Another ironic ending.