Undoubtedly the most important elements in the foregoing tale of work are those relating to the mammalian (and especially the marsupial) brain, and the marsupial dentition. And if Flower had accomplished nothing more than this, he would have been entitled to gratitude of his successors. But, as we shall immediately see, all the above formed but a portion of his zoological labours. CHAPTER VI WORK ON THE CETACEA Next at any rate to the study of the various races of the human species (which he took up seriously later on in his career), the group of mammals to which Flower devoted special attention, and which attracted his greatest interest, was undoubtedly that of the Cetacea, or whales, dolphins, porpoises, etc. At the time when he set himself seriously to study these aquatic and fish-like mammals, the zoology of the group was certainly in a most confused and unsatisfactory state; partly, no doubt, owing to the comparative rarity of complete specimens in our museums, and the consequent difficulty of instituting accurate comparisons, and partly to the reckless prodigality with which names had been given to imperfect or insufficiently characterised specimens by some of his predecessors and early contemporaries, and the needless multiplication of generic terms. It was consequently at this time almost impossible to be sure which was the right name for even many of the commoner species; while in the case of the rarer kinds, the confusion was almost hopeless. When Flower left the subject—which he only did when his working days were over—it was in great measure thoroughly in order, although of course much was left for future workers to fill in. Unhappily, his views on the nomenclature of the group have not been accepted by all his followers; so that a fresh and totally unnecessary source of confusion has been introduced of late years into a subject which had already sufficient difficulties of its own. In regard to the discrimination of species, Flower took a view almost the reverse of that held by some of his predecessors and colleagues; and, as he says himself, he may have consequently erred in a direction the very opposite of theirs. “As species have not generally been recognised as such,” he wrote in the British Museum _List_ of 1885, “unless presenting constant distinguishing characters capable of definition, it is probable that, in the imperfect state of knowledge of many forms, some may have been grouped together which a fuller acquaintance with all parts of their structure, external and internal, will show to be distinct.”