Imagine that in a jar of muddy water you see a greenish entity with small sprouting parts: a weird little thing that looks like it is part of a small plant. You detach it and cut it in two, and each part grows again, each with its branching appendages. In 1740, you might well have concluded that this was a small plant itself. But if it begins to move from place to place, you might have second thoughts. It turns out that this tentacular organism is in fact a creature that can reproduce itself by simple subdivision.
This tiny organism had been observed under a microscope before, but the discovery that it is in fact a multi-headed animalicule that can reproduce itself asexually was made by Abraham Trembley (born: 3 September 1710) in Geneva, Switzerland. He was the one who first cut the creature in two, and observed each portion grow its own many heads, reminding one of the legendary polycphalous Hydra of Greek mythology. Recall that the monster promptly grew a new head when one of these was severed by the heroic Heraklites (Hercules). So this newly discovered biological entity came to be called hydra also. The myth-maker probably never imagined there really is such an animal in the natural world.
Trembley studied hydra in detail. In fact, he recognized that there are three different kinds of them. Today we know that hydra also develop testes and ovaries and mate to propagate. The female hydra holds on to the embryo until the latter breaks away and becomes altogether independent.
Hydra have only one leg, but five or more arms (tentacles) an orifice in the center that serves as mouth. Into that tiny mouth it shoves periodically its microscopic food. While it is digesting the food, the tentacles are brought close to the main body. Biologists tell us that hydra feed on tiny shrubs called daphnia, minute crustaceans called copepods, and sometimes they even devour very small fish.
Trembley was a careful and ingenious experimenter, and a meticulous observer too, which is why some have called him “the father of experimental zoology.” His work revealed the phenomenon of reproduction of an animal through budding, as with a flower: quite a remarkable process when it was first observed. The locomotion of the hydra is interesting to watch. It looks as if they are doing a somersault.
In 1744, Trembley published a book on hydra which he described as a kind of soft-water polyps with horn-like arms (polypes d’eau douce à bras en forme de cornes). He was also one of the first to actually observe cell-division under a microscope, though it was not recognized as such.
Hydra are among the countless life forms which have emerged from the random mutation of genes in the long and tortuous creativity of biological evolution. What role these many-headed mini-monsters play in the biosphere, we do not know for sure. They make less of a splash than us humans, perhaps, in the indifferent silence of nature, but they add in their own way to the grand orchestra of terrestrial life.
Our inquisitive probes into the splendor of the world around have brought to light countless things: from the small and hardly visible hydra of the waters to the vast Hydra of the heavens (as one of the sprawling constellations is called), and both have derived their names from the limitless realm of human imagination: Greek mythology in this case. Though most people who have experienced a first course in biology may have heard of the aquatic hydra, not many may know that Abraham Trembley was one the first to have studied it with thoroughness.
October 17, 2013