quality:correction
Voyage of the Rattlesnake

Aged 20, Huxley was too young to apply to the Royal College of Surgeons for a licence to practise, yet he was "deep in debt". So, at a friend's suggestion, he applied for an appointment in the Royal Navy. He had references on character and certificates showing the time spent on his apprenticeship and on requirements such as dissection and pharmacy. William Burnett, the Physician General of the Navy, interviewed him and arranged for the College of Surgeons to test his competence (by means of a viva voce).

Finally, Huxley was made Assistant Surgeon ('surgeon's mate', but in practice marine naturalist) to HMS Rattlesnake, about to set sail on a voyage of discovery and surveying to New Guinea and Australia. The Rattlesnake left England on 3 December 1846 and, once it arrived in the southern hemisphere, Huxley devoted his time to the study of marine invertebrates. He began to send details of his discoveries back to England, where publication was arranged by Edward Forbes FRS (who had also been a pupil of Knox). Both before and after the voyage Forbes was something of a mentor to Huxley.

Huxley's paper "On the anatomy and the affinities of the family of Medusae" was published in 1849 by the Royal Society in its Philosophical Transactions. Huxley united the Hydroid and Sertularian polyps with the Medusae to form a class to which he subsequently gave the name of Hydrozoa. The connection he made was that all the members of the class consisted of two cell layers, enclosing a central cavity or stomach. This is characteristic of the phylum now called the Cnidaria. He compared this feature to the serous and mucous structures of embryos of higher animals. When at last he got a grant from the Royal Society for the printing of plates, Huxley was able to summarise this work in The Oceanic Hydrozoa, published by the Ray Society in 1859.

The value of Huxley's work was recognised and, on returning to England in 1850, he was elected a Fellow of the Royal Society. In the following year, at the age of twenty-six, he not only received the Royal Society Medal but was also elected to the Council. He met Joseph Dalton Hooker and John Tyndall, who remained his lifelong friends. The Admiralty retained him as a nominal assistant-surgeon, so he might work on the specimens he collected and the observations he made during the voyage of the Rattlesnake. He solved the problem of Appendicularia, whose place in the animal kingdom Johannes Peter Müller had found himself wholly unable to assign. It and the Ascidians are both, as Huxley showed, tunicates, today regarded as a sister group to the vertebrates in the phylum Chordata. Other papers on the morphology of the cephalopods and on brachiopods and rotifers are also noteworthy.