Why Blind Tadpoles and Put Eyes In Their Tails?

Tadpoles are often used to teach students about the cycle of life as they go through a very visible metamorphosis, literally changing their form as they mature into frogs. Tadpoles can regrow their tails, a regenerative ability that makes them useful for scientific study. But some of this research raises some ethical qualms, including a recent experiment in which scientists implanted an eye from one tadpole into the tail of another.

Yes, that sounds at least like science fiction of the troubling kind. Tadpoles and frogs have long been used in scientific experiments. As they are vertebrates without an egg shell, their development can be readily observed from the embryo stage onward and some species are easily raised in captivity. They also reach reproductive age in just a few months, so studies across generations are possible in a short period of time.

Tadpoles Into Frogs

Born from clusters of a few to several hundred jelly-like eggs with gills like fish, some tadpoles become frogs in a few weeks, while others do so in months. Tadpoles at first consist mostly of a head and a tail. They eat voraciously — metamorphosis takes a lot of energy — and start to grow back legs (you can get an idea of the many varieties of tadpoles in the southeastern U.S. from this guide).

Tadpoles’ front legs are the next to form, along with changes in their internal organs: they acquire lungs so they can breathe air and their digestive systems change. While adult frogs are carnivores, tadpoles are omnivores who eat algae, rotting vegetation and (survival of the fittest) other tadpoles.

In the wild, frog eggs and tadpoles are themselves eaten by fish, birds and other animals; most tadpoles do not survive into adulthood. They have developed some adaptations to improve their chances, such as their flexible tail that, when caught by a predator, tears easily. In fact, a tadpole can still swim even when it loses as much as a quarter of its tail. Tadpoles can then regrow their tails and one study suggests that (especially when stressed by prolonged predator attacks), they grow larger tails.

Tadpole Eyes Implanted in Tadpole Tails

Implanting one tadpole’s eye into the tail of another takes this regenerative ability into quite another direction. In an experiment, scientists at Tufts University transplanted eyes from tadpole embryos onto the tails of other tadpoles who had been blinded. The tadpoles were found to be able to see from the eyes in their tails.

The purpose of this experiment is to see how well a “displaced eye” can see, to help scientists in developing software for robots (who would be able to “see” from many of their different parts) and also  in creating prosthetic sensory organs (perhaps even an eye that could, indeed, help a person to see).

But now, in a lab at Tufts University, there are apparently frogs that have eyes on their derričres. It’s a “transformation” in the name of science and of creating new technologies to help us. But talk about a disruption of the usual development of tadpoles!

The natural metamorphosis that tadpoles undergo is one explanation for folktales of frogs being able to change their form, like that of the frog prince who becomes human after a princess kisses him. Eyes implanted on their hindquarters seems more like a horror story. Are some experiments, even if they’re intended ultimately to benefit humans’ health, going too far, altering what nature made in unnecessary ways?


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Photo from Thinkstock


.4 years ago

very,very sad,thank you for sharing

Carrie-Anne Brown

very sad but thanks for sharing

Connie O.
Connie O4 years ago

Thank you for the article.

Sheri D.
Sheri D4 years ago

I am against all animal testing.

Lynda H.
Lynda S4 years ago

Susan M, I am as entitled to express my opinion on these threads as you are, and I do so without rudeness. Telling someone to “shut up” is extremely immature, rude and well outside the Care2 Code of Conduct.

You resort to insults because you don’t have the words to back up your implanted conviction. You cannot discuss, debate or argue when you have no personal experience as a foundation, only animal rights propaganda.

As I have said several times before: all pharmaceuticals and medical procedures must, by law, be tested on animals first. If there are no dangerous reactions, the tests are then conducted on humans. These tadpole tests are teaching us about brain plasticity, so far at an embryonic stage: you would approve of a human baby being blinded and having an eye transplanted near its spine? And you want to lecture ME on ethics?!

Nimue Pendragon

Stop all vivisection now, it's wrong.

Susan M.
Susan M4 years ago

Lynda H - shut up please

If we want to experiment for human benefit we experiment on humans, not make countless other species suffer on our behalf

People like you ensure this sort of abuse of animals will continue because you use the same old arguments about children blah blah


Who the hell are we to abuse animals in this way? I think there is something morally wrong with people who think this sort of treatment of another species is acceptable

Lynda H.
Lynda S4 years ago

Christine J, it would not irrelevant if you or your child was visually impaired or facing blindness. Nor would it be irrelevant if you just suffered a stroke or paralysis through injury, because although these experiments are focused on sight, the knowledge gained will lead to treatments and cures for many diseases, conditions and injuries connected with the brain and nervous system.

Virtually every medical advance over the past century was only made possible through testing on animals. The biology of life is the same regardless of differing physiology. It is unethical to allow hundreds of millions of innocent people AND animals to suffer when we can find cures, successful treatments, vaccines or prevention using a few animals. Animals do not suffer in the lab: there are strict protocols and laws to protect them.

Animal rights groups use photographs from other countries, from over 50 years ago, and even those that are staged - where the animal is deliberately abused by an animal rights spy for the camera. They tell lies to manipulate you into supporting them. Your support will help to bring about a world where there are no more medical breakthroughs and no cats or dogs. Do you know that? Do you want that?

Christine Jones
Christine J4 years ago

It is completely irrelevant what the purpose of the experiment was, and whether it might in the future help some humans or not. Firstly, we know from experience that the majority of animal experiments are completely useless, or worse, actually misleading, particularly when the species used is radically different from humans. Secondly, it is unethical to commit such horrors on any living creatures. Good can never come from cruelty.

Katie K.
Katie K4 years ago

I hated biology class when we had to cut up dead animals. I realize it can be important to save some humans but aren't we meant to fellow our own individual paths.