Bathybius haeckelii was a substance that British biologist Thomas Henry Huxley discovered and initially believed to be a form of primordial matter, a source of all organic life. He later admitted his mistake when it proved to be just the product of a chemical process (precipitation).
In 1868 Huxley studied an old sample of mud from the Atlantic seafloor taken in 1857. When he first examined it, he had found only protozoan cells and placed the sample into a jar of alcohol to preserve it. Now he noticed that the sample contained an albuminous slime that appeared to be criss-crossed with veins.
Huxley thought he had discovered a new organic substance and named it Bathybius haeckelii, in honor of German biologist Ernst Haeckel. Haeckel had theorized about Urschleim ("primordial slime"), a protoplasm from which all life had originated. Huxley thought Bathybius could be that protoplasm, a missing link (in modern terms) between inorganic matter and organic life.
Huxley published a description of Bathybius and also wrote to Haeckel to tell him about it. Haeckel was impressed and flattered and procured a sample for himself. In the next edition of his textbook The History of Creation Haeckel suggested that the substance was constantly coming into being at the bottom of the sea. Huxley did not agree but speculated that Bathybius formed a continuous mat of living protoplasm that covered the whole ocean floor.
Other scientists were less enthusiastic. Charles Wyville Thomson examined some samples in 1869 and regarded them as analogous to mycelium. George Charles Wallich claimed that Bathybius was a product of chemical disintegration.
In 1872 the Challenger expedition began; it spent three years studying the oceans. The expedition also took soundings at 361 ocean stations. They did not find any sign of Bathybius, regardless of the claim that it was a nearly universal substance.
In 1875 ship's chemist John Young Buchanan analyzed a substance that looked like Bathybius from an earlier collected sample. He noticed that it was a precipitate of calcium sulfate from the seawater that had reacted with the preservative liquid (alcohol). Buchanan suspected that all the Bathybius samples had been prepared the same way and notified Thomson, the leader of the expedition. Thomson sent a polite letter to Huxley and told about the discovery.
Huxley realized that he had been too eager and made a mistake. He published part of the letter in Nature and recanted his previous views. Later, during the 1879 meeting of the British Association for the Advancement of Science, he stated that he was ultimately responsible for spreading the theory and convincing others. Most biologists accepted this acknowledgement of error.
Haeckel, however, did not want to abandon the idea of Bathybius because it was so close to proof of his own theories about Urschleim. He claimed without foundation that Bathybius "had been observed" in the Atlantic. He continued to support this position until 1883.
Huxley's rival George Charles Wallich, in turn, claimed that Huxley had committed deliberate fraud and also accused Haeckel of falsifying data; Haeckel did draw a series of pictures of the evolution of his Urschleim, supposedly based on observations. Other opponents of evolution, including the Duke of Argyll and modern creationists, have tried to use the case as an argument against evolution in general.
Ley, Willy (1959). Exotic Zoology. New York: Viking Press.