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Worm Decapitation

Natalie Sell | February 22, 2019

The misconception that cutting an earthworm in half will produce two worms has been floating around for years. In reality, if you cut an earthworm in half, there are two possible outcomes: 1.) the worm dies, or 2.) you get one shorter worm.

Earthworms can regenerate their tails up to a certain point, so the tail half would die while the front would begin regrowing a tail. As long as the worm is cut below the clitellum (the swollen band near the front), it will survive. Earthworms store most major organs between the head and this band.

Although the common earthworm will not produce two worms if cut in half, other “worms” can; namely, the planarian flatworm. This flatworm’s regenerative ability lies in its adult stem cells. Each stem cell is capable of restoring an entire worm, which means that planarian flatworms can do far more than turn into two when cut in half. In fact, planarian flatworms can be cut into 279 pieces, each of which will grow into a complete worm.

The flatworm’s ability to regenerate its brain is unusual; even more shocking is that it seems to recover memories as well. Worms that regenerated from originals (which were previously taught how to eat in a controlled setting) were able to relearn these skills significantly faster than others. Scientists think this ability may lie in the distribution of the worm’s nervous system, although they still have countless unanswered questions. Even so, flatworms could reveal new ways of studying learning and memory.

We can learn from flatworms in more ways than one. A team at the Stowers Institute for Medical Research has developed new methods of researching regeneration. Flatworms don’t have a distinct separation of body parts, so it’s difficult to keep methods constant when working with multiple flatworms. However, this team of scientists created a method of chemical amputation that damages each worm in precisely the same area. They can observe which genes activate, thereby revealing which genes correspond to each portion of the flatworm.

The specificity of this study could allow scientists to examine the details of regeneration, and perhaps eventually learn how to apply these qualities to the medical world. Stem cell research has the potential to yield fascinating results with a major impact on treatment and healing in the future, and flatworms could help advance our knowledge. While there’s still a long way to go in terms of understanding how to apply this information to human medicine, it’s evident that there’s a lot we can learn from worms.

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