Previously, I wrote a blog about the reintroduction of Rhinoplasty to European surgery in the early 19th century by Joseph Constantine Carpue. The idea of transplanting tissue had been neglected for such a long time in Europe, and I wanted to try to explore why that might be in that blog post as well as discuss Carpue’s achievement. However, while I was researching it, I came across many interesting tangents about transplantation and ideas about regeneration in history. Due to space, I didn’t elaborate then, but I wanted to come back to some of the subjects I touched on and give them their own space – the subjects of this blog, polyps, are one of those tangents.

Polyps, often called Hydra, are very strange tiny creatures who live in freshwater. They have a simple tubular body and their head is surrounding by fine little tentacles, and they have continued to fascinate students of biology since their discovery with their extraordinary capabilities. They were actually first documented by the great 17th century microscopist Jan Van Leeuwenhoek, who had published about them in the Philosophical Transactions of the Royal Society in 1702/3. However, it actually took the observations of a Swiss naturalist in the 1740s to really propel Polyps into the scientific spotlight.

Abraham Trembley was born in 1710 in Geneva, and his father was one of the highest ranked officials in the politics of the Republic during a period of instability. For his higher education, Trembley studied philosophy, theology and calculus at the Calvin Institute (now the University of Geneva). He seems to have considered ministry after graduation, but instead he became the tutor to the children of Willem Bentinck van Rhoon, the Count of Bentinck while the Count and his wife were going through a divorce and were rarely with them. Trembley and his pupils, amongst other lessons, walked in the estates and collected insects and plants to look at from the land and the waters, and it was on one of these expeditions that the party collected polyps – which appeared to be exceedingly tiny little plants – in a jar of water.

Trembley wondered, however, from its behaviour, if the polyp was an animal or a plant, as did his long-time correspondent, the great French naturalist Réaumur (who actually named the polyps, for their resemblance to an octopus). The polyp looked like a plant – and plants in water can often move – but Trembley (and the children he was tutoring) saw it ‘walk’ by a rolling motion, and eat by hunting and capturing prey in its ‘arms’ and feeding it to a central stomach. So Trembley did an experiment to determine whether the polyp was a plant, or indeed an animal.

Plants which are cut, Trembley reasoned, can redevelop and grow new

Drawing of Polyp.

from the cutting, but animals will die. So Trembley cut a polyp in half and expected it to die, proving it was an animal. But it didn’t die. Instead, whole new polyps developed out of the two new halves and the new polyps displayed all the same abilities as the original one. Trembley went on to discover that no matter how you cut the polyp – in half vertically or horizontally, into small parts or into many pieces – new polyps would always grow from the parts and become fully functioning new polyps. At one point, Trembley had 36 polyps, all developed out of cut parts from one original body. In another test, Trembley actually turned a polyp inside out, pulling from its stomach with a bristle. Instead of dying, the Polyp just grew a new outside layer.

The polyp also initially appeared to reproduce asexually. As well as regenerating into new creatures when deliberately cut, the polyp would also naturally develop buds which would grow into new polyps, in a way similar to the budding seen in plants. However, Trembley and his correspondents also searched carefully for the presence of eggs and eventually found them. To make the nature of the polyp yet more confusing, the polyp reproduced in both ways, by budding and with eggs and sperm, when it was in difficulties. Trembley’s cousin Charles Bonnet would go on to speculate that the polyp is a true link between the plant and animal worlds with its mixture of behaviours and abilities.

Trembley wrote extensively to his correspondents Réaumur and Bonnet about the polyps and they speculated about his discoveries together. But In order to ensure that his correspondents and contemporaries could see the polyps for themselves, Trembley also managed to send live specimens – the polyps travelled in a jar on horseback. This process benefitted Trembley when he published, having already received the agreement already of many important men concerning his observations. The publication also led to a small craze in which many educated gentlemen kept their own tank of polyps in order to observe them too.

The remarkable polyp, when these discoveries were revealed, didn’t only prove to be a challenge to everything that had previously been understood about the way an animal body works – or can work – biologically. It provided new dilemmas – or new possibilities – to those who were interested in the soul and in Creation philosophically and theologically. Hydra seemed to challenge all the acceptable Christian ideas about reproduction and it seemed to have reproductive – and regenerative – force distributed through its whole body. What happened to this animal’s soul when it was being cut in half and forming perfectly into two beings?

But how does the polyp continue to be influential in the thinking of scientists today and what light has modern science been able to throw on their mysterious lives? Scientists today are indeed still publishing papers on Trembley’s polyps in a wide range of journals and are still pondering its apparent biological immortality. Recently, the polyp’s genome has been mapped and the polyp has revealed some of the secrets of its incredible cells and genes, including the way in which the hydra’s cells (like as-yet unspecialised stem cells) renew themselves continually, and the presence of a protein called FoxO in all its cell lineages. This protein, which has also been demonstrated to be active in many human centenarians, plays a role in human longevity too. Study of the polyp might be able to show us the way to slow, or at least better understand senescence (the process of aging in cells), a process polyps don’t seem to display at all. It’s a possibility that study of the polyp’s lack of senescence and its regenerative capabilities could also lead to a breakthrough in understanding and maybe reversing the effects of neurological diseases like Alzheimer’s.

Trembley was quite right when he identified his ‘little machines’ as being significant and extraordinary some 270 years ago. 


Baker, John Randal. (Arnold, 1952). Abraham Trembley of Geneva: Scientist and Philosopher, 1710-1784.

Boehma, Anna-Marei, Konstantin Khalturina, Friederike Anton-Erxlebena, Georg Hemmricha, Ulrich C. Klostermeierb, Javier A. Lopez-Quinteroa, Hans-Heinrich Obergc, Malte Pucherta, Philip Rosenstielb, Jörg Wittlieba, and Thomas C. G. Boscha. “FoxO is a critical regulator of stem cell maintenance in immortal Hydra.”Proceedings of the National Academy of Sciences of the United States of America (PNAS). 

Bosch, Thomas C.G.Why polyps regenerate and we don’t: Towards a cellular and molecular framework for Hydra regeneration.

Dinsmore, Charles E., ed. 2007. A History of Regeneration Research: Milestones in the Evolution of a Science. Cambridge University Press. 

Ingram, Jay. 2016. The End of Memory: A natural history of ageing and Alzheimer’s. Random House.

Lenhoff, Sylvia G.,  Howard M. Lenhoff, and Abraham Trembley. 1986. Hydra and the birth of experimental biology, 1744: Abraham Trembley’s Mémoires concerning the polyps. Boxwood Press.

Moore, Keith.Hydra meets Handel. 27 March 2014. Accessed 17 August, 2017. 

Trembley, Abraham. 1744. Mémoires pour servir à l’histoire d’un genre de polypes d’eau douce. 

Trembley, Abraham. (Libreirie Georg., 1985). From Trembley’s Polyps to New Directions in Research on Hydra: Proceedings of a Symposium Honoring Abraham Trembley (1710-1784).

Kirsty Chilton is assistant curator at the Old Operating Theatre Museum and Herb Garret. She is not too fond of selfies, hence the lego Resurrection Man

Polyps: A Real Life Hydra in Miniature
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