The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
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Epigenesis is development from an embryo with the sequential appearance of tissues and organs. The tissues and organs differentiate from a population of equivalent (undifferentiated) embryonic cells which in turn descended from a single cell, the zygote. The concept holds that a relatively formless egg gives rise to the highly structured adult organism. Epigenesis is to be distinguished from preformation, which is the notion that organisms are fully formed but minuscule in the sex cells. Curiously, some preformationists were animalculists who thought they saw a fully formed human in the head of a sperm cell. Others, known as ovists, believed that eggs contain the miniature human. To be logical, the fully formed "homunculus" that existed in either the egg or sperm must have had within it sex cells with even more tiny formed humans. And those tiny humans must have had all future generations encased in their sex cells as ever more tiny "homunculi". Obviously, this was nonsense. Both animalculists and ovists were completely in error. With the development of the light microscope, it became obvious that egg cytoplasm was devoid of tissues and organs and, of course, the head of a sperm was comprised almost entirely of the nucleus. Actually, early observers were epigenetic. Aristotle (384-322 B.C.) and William Harvey (1571-1657) looked at the developing chick. They did not see a chicken in the egg. Rather, they saw a developing embryo that gradually became more complex with time. These early observers clearly reported the epigenetic development of chick embryos.