The Contents of this late forties, early fifties work follows:7 • Introduction (Assignment in Tomorrow) • (1954) • essay by Frederik Pohl
9 • Mr. Costello, Hero • (1953) • novelette by Theodore Sturgeon
35 • Angels in the Jets • (1952) • short story by Jerome Bixby
47 • The Adventurer • (1953) • short story by C. M. Kornbluth
61 • Subterfuge • (1943) • short story by Ray Bradbury
70 • Helen O'Loy • (1938) • short story by Lester del Rey
82 • 5,271,009 • (1954) • novelette by Alfred Bester
117 • The Big Trip Up Yonder • (1954) • short story by Kurt Vonnegut, Jr.
132 • We Don't Want Any Trouble • (1953) • short story by James H. Schmitz
140 • The Peddler's Nose • [Quarantine] • (1951) • short story by Jack Williamson
155 • The Frightened Tree • (1953) • short story by Algis Budrys (variant of Protective Mimicry)
166 • A Matter of Form • (1938) • novella by H. L. Gold [as by Horace L. Gold]
229 • Back to Julie • (1954) • short story by Richard Wilson
234 • She Who Laughs ... • (1952) • short story by Peter Phillips (variant of She Who Laughs)
249 • Official Record • (1952) • novelette by Fletcher Pratt
267 • Hall of Mirrors • (1953) • short story by Fredric Brown
274 • Mother • (1953) • novelette by Philip José Farmer?

There is not that much published in this genre by Fletcher Pratt, so this should come to the attention of the completists among us. ( )