Expert: Jedediah - 12/17/2005

Question
Sir,

I have read that the cut part of a starfish can regenerate into an entire new starfish. Why is a lizard's tail not able to do the same?

Thankyou.

Saad.

Answer
Dear Saad,
thank you for your question.
Not all species of starfish can do this. Most of them can only regenerate body parts and if cut in half, the side that has the vital organs survives, the other dies, like with earthworms.
The tail of a lizard is not able to survive without the rest of the body, it relies for example on the heart to supply the blood and the brain and the backbone to tell it what to do ect. Startfish have no backbone and only a very primitive brain, so the bodyparts are much more independent and the cells are more fexible, as with all invertebrates. If an invertebrate looses a bodypart, it can regrow it (some all their life, some only as juveniles) because the cells have the ability to divide. With the starfish you asked about, the cells not only divide, but some of them turn into different cells, so a cell cluster that was formerly part of a leg can turn into a stomach. Mammals are able to do this  very early in their life, when the embryo is still just a cell cluster. If cut in half, both halfs will develope into a normal animal (or human). The cells loose that ability later.
For more extensive information on this, I recommend Wikipedia or other encylopedias.
http://en.wikipedia.org/wiki/Category:Biological_reproduction
http://en.wikipedia.org/wiki/Biological_life_cycle
I hope I was of some help to you
Jennifer