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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 Development in Different Animal Taxa


Development in Different Animal Taxa:
As discussed in a previous chapter, animals can be divided into three major groups according to how they develop. In the sponges (Phylum Porifera) and similar animals, there is no embryonic development at all. These animals have no true tissues, and it’s not an exaggeration to say that they’re basically just clumps of cells. These animals are sometimes referred to as the Parazoa (“beside-animals”), indicating that they split off from the main line of animal evolution (the Eumetazoans) very early.



Development in a sponge: There is no gastrulation and, therefore, no embryonic tissues form. As
a result, the adult animal is basically a clump of largely undifferentiated cells with no true tissues or organs.

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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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