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Animal body plans

The embryos of vertebrates (animals with backbones) pass through a common stage early in their development. At this stage they show strong similarities, although the animals come to be as different as a human and a cat. This happens as their body plans are being laid down. It seems that an efficient way of marking out the body plan arose millions of years ago, and has remained virtually unchanged throughout animal evolution.

At early stages in their development cat, bat and human embryos share remarkable similarities.
At early stages in their development cat, bat and human embryos share remarkable similarities.
2005 M K Richardson

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