In the latter decades of the nineteenth century Thomas Henry Huxley was at the heart of British Science: President of the British Association for the Advancement of Science (1870), President of the Royal Society (1883-86), Chairman of innumerable committees. His thought in many ways characterises the spirit of the 'high' Victorian age in Britain. He was not only the most eminent academic biologist of his time but also deeply interested in philosophical issues. His re-examination of the evolution of the brain in response to Richard Owen's 'telenomic' views formed the kernel of the notorious debate at the 1860 meeting of the British Association in Oxford. From his early youth until old age he thought long and hard about the mind/body problem. This paper follows the development of his ideas and shows how in debate with many of the leading thinkers of his age, in the X-club and the Metaphysical Society, he struggled to develop a biologically-based account of the relationship between mind and brain. However, at the end, he seems to have recognized that his position was not entirely satisfactory and ultimately famously confessing himself 'agnostic' turned from metaphysics to devote himself to more practical issues. The unresolved problems of mind and brain which perplexed Huxley remain to torment his epigoni.