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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 Eumetazoan Development


In the Eumetazoa (“true animals”), hox genes are present, which help to regulate developmental processes. All of the eumetazoans have embryonic development – that is, gastrulation occurs early in development, leading to the formation of embryonic germ tissues. These tissues ultimately form the tissues and organs of the adult animal’s body.

The Radiata (Phyla Cnidaria and Ctenophora) are diploblastic, meaning that only two germ tissues form during gastrulation – endoderm and ectoderm. Since mesodermal tissue does not occur in these animals, they have no mesodermal organs. Consequently, their bodies are relatively simple, though they do have true tissues, unlike parazoans.

The Bilateria are triploblastic, meaning that three germ tissues form during gastrulation. Since these animals have internal organs that form from mesodermal tissue, their bodies are much more complex than are those of the radiate animals. Depending on how their early development occurs, triploblastic animals are either protostomes (“mouth first”) or deuterostomes (“mouth second”).


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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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