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An Introduction to Zoology:  Chapter 6
An Introduction to Zoology: Chapter 6
Published by The Lone Ranger
08-07-2008
Default Preformation

Preformation:
Before the invention of microscopes, and especially before it was possible to directly view what happens during fertilization and early development, preformationist theories were frequently used to explain animal development. According to preformationism, either the egg or the sperm contained a complete, “pre-formed” individual inside of it, called a homunculus (from the Latin for “little man”). As such, development was simply a matter of the homunculus growing larger. Whether the homunculus was contained in the sperm or the egg was a matter of considerable debate.

The notion that the homunculus was contained in the sperm was known as spermatism or animalculism. (“Animalcule” means “little animal,” so “animalculism” was the notion that each spermatozoan contained a tiny, already-formed animal.) The notion that the homunculus was contained in the ovum was known as ovism.

Some vestiges of preformationist notions have survived even to the present day. For instance, even today, it’s not uncommon to refer to semen as a man’s “seed.” At one time, it was commonly believed that sperm were, in effect, seeds that “took root” in a woman’s womb and grew into a baby there. Of course, it was obvious that the woman contributed something to the baby’s makeup, so it was generally assumed that an individual’s growth and development would be influenced by the environment in which they occurred. That is, the “seed” of a given man would produce children that looked distinctly different if they happened to grow in the wombs of different women.

Similarly, we still use the term “fertilization,” which comes from the notion that the primary function of a man’s semen is to “fertilize” the woman’s womb, which is otherwise “barren.” According to this notion, the function of fertilization is not so much to contribute genetically to a future offspring, but rather to provide the “fertilizer” that makes it possible for the homunculus the woman is already carrying to start growing and thus become a baby.



A 1694 diagram of a spermatozoan,
showing a pre-formed homunculus inside.

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  #1  
By monruw on 03-30-2011, 01:55 PM
Default Re: An Introduction to Zoology: Chapter 6

why it's called animal-vegetal axis? sound like kinda food, meat and vegetable or what else~ any story behind this?
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  #2  
By The Lone Ranger on 05-22-2011, 01:35 AM
Default Re: An Introduction to Zoology: Chapter 6

"Vegetal," is related to "vegetable." Many plants can reproduce asexually, whereas virtually all animals reproduce sexually.

Probably for this reason, "vegetal" came to refer to processes in living things that are "plant-like," especially processes that do not occur through sexual reproduction. More to the point, perhaps, plants generally grow much more slowly than do animals. So the "vegetal" pole of an egg gets its name for the fact that the cells in this region grow and divide much more slowly than do the cells in the "animal" pole.


Cheers,

Michael
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