Vertebrates

The animals we know best for man is one of them-are called vertebrates, or animals with a backbone (vertebra, Latin for a twisting joint) there are five classes: mammals, birds, reptiles, amphibians and fishes. Some zoologists give this group another name, the Chordata, so as to include a few very primitive sea- creatures like sea- squirts and lampreys which also have a kind of simple backbone, called notochord. In the true vertebrates this is found in the embryos only(when the animal is in its earliest stage of development and is slowly replaced by a bony, jointed vertebral column down the back.