Planaria are little flatworms with triangle heads, beady eyes, and the ability to regenerate after being cut in half. Bet you didn’t expect that last part, did you? Unlike cell division, planarian fission is violent and … well, weird. To stimulate these little guys to split, you have to first decapitate them.

Unlike mitosis, planarian binary fission is simpler. There are no chromosomes that form or mitotic spindles. The worm simply holds on to a surface with its pharynx, uses peristalsis to create a waist, and pulsating muscular contractions rip the worm in half. The tighter the worm is able to hold on, the easier it is to tear itself apart.


What happens to the resulting two parts? Stem cells spring into action and within a week, you’ll have two new worms! Keep this up and you may find yourself with a little farm of planaria. If you want to try this little experiment yourself, planaria are easy to find in soil from ponds and lakes. Suck out a few of these guys (they are visible to the naked eye) and put them in a separate dish. You can keep them alive by feeding them chopped up egg yolks.

Aside from being a super cool merge of physics and biology, this study on planarian fission can give scientists new insights into tissue regeneration. And plus, I bet at least one person signed up because the job description involved worm decapitation.