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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 Holoblastic Cleavage


As mentioned, the amount of yolk in an egg and its distribution affect how cleavage occurs. In animals that have isolecithal eggs, because the cells have so little yolk, cleavage is holoblastic (from the Greek “holo,” meaning “whole” and “blastos,” meaning “germ”). In holoblastic cleavage, each cleavage extends all the way through the egg, completely dividing it.



A sea urchin (Phylum Echinodermata) has isolecithal eggs and
holoblastic cleavage. Each cleavage completely divides the egg.

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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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