A Gun for Dinosaur originally appeared in Galaxy Science Fiction, March 1956. © 1956 by Galaxy Publishing Corporation. Reprinted in The World That Couldn't Be and 8 Other Novelets from Galaxy; edited by H. L. Gold.
Aristotle and the Gun originally appeared in Astounding Science Fiction, February 1956. © 1956 by Street & Smith Publications, Inc. The Guided Man originally appeared in Startling Stories, October 1952. Copyright 1952 by Better Publications, Inc.
Internal Combustion originally appeared in Infinity Science Fiction, February 1956. © 1955 by Royal Publications, Inc.
Cornzan the Mighty originally appeared in Future Science Fiction, No. 28. © 1955 by Columbia Publications, Inc.
Throwback originally appeared in Astounding Science Fiction, March 1949. Copyright 1949 by Street & Smith Publications, Inc.
Judgment Day originally appeared in Astounding Science Fiction, August 1955. © by Street & Smith Publications, Inc. Reprinted in The Best Science Fiction Stories and Novels, edited by T. E. Dikty.
Gratitude originally appeared under the title Property of Venus in Galaxy Science Fiction, July 1955. © 1955 by Galaxy Publishing Corporation.
A Thing of Custom originally appeared in Fantastic Universe Science Fiction, January 1957. © 1956 by Ring-Size Publications, Inc. Reprinted in Fantastic Universe Omnibus, edited by Hans S. Santesson.
The Egg originally appeared in Satellite Science Fiction, October 1956. © 1956 by Renown Publications, Inc.
Let's Have Fun originally appeared in Science Fiction Quarterly, May 1957. © 1957 by Columbia Publications, Inc.
Impractical Joke originally appeared in Future Science Fiction, No. 29. © 1956 by Columbia Publications, Inc.
In-Group originally appeared in Marvel Science Fiction, No. 30. Copyright 1952 by Stadium Publishing Corporation.
New Arcadia originally appeared in Future Science Fiction, No. 30. © 1956 by Columbia Publications, Inc.
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