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An Introduction to Zoology:  Chapter 6
An Introduction to Zoology: Chapter 6
Published by The Lone Ranger
Default The Allantois

The Allantois:
The allantois is similar to the yolk sac in that it originates as an outgrowth of the embryonic gut. Its primary function is to store metabolic wastes generated by the developing embryo. In many amniotes, itís also important in gas exchange, as it partially fuses with the chorion to produce the chorioallantoic membrane. The base of the allantois develops into the urinary bladder.

In those amniotes that remain inside the egg while developing, the importance of the allantois cannot be overestimated. Not only is it important in gas exchange, but it stores and isolates poisonous metabolic waste products that would otherwise kill the developing embryo. (The shell that surrounds the egg prevents the embryo from expelling wastes.)

In placental mammals, the allantois plays a much less important role, since the embryoís metabolic wastes are transported away by the motherís blood.


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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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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.


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