The species of flatworm seems to have an astonishing ability to repair its cells and replace the old ones with the new ones and the new ones then subsequently age. Researchers from the University of Nottingham studied that aging seems to be defined by telomere length. In case of the stem cells of the flatworm species, the telomere length of the DNA strand after regeneration seems to be same as those before. In a nutshell, this means that the flatworm can replace its cells endlessly. How they do it is still a mystery for the scientists.