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 types of structure ; and his aim was that every student should be enabled to test general statements concerning a group of animals by reference to one member of the group which he had been made to know thoroughly. Huxley realised from the first that the thorough knowledge of representative animals, which is the only proper foundation for a knowledge of morphology, ought to be acquired by direct observation in the laboratory ; this, however, was impossible in Jermyn Street, and his ideal was not completely realised until later. In spite of a certain distaste for public speaking, which only time and practice enabled him to overcome, he devoted much of his most strenuous effort to the work of popular exposition. In a letter dated 1855 he says, 'I want the working classes to understand that science and her ways are great facts for them — that physical virtue is the base of all other, and that they are to be clean and temperate and all the rest — not because fellows in black with white ties tell them so, but because these are plain and patent laws of nature, which they must obey under penalties.'

His scientific work during this period was influenced by his official duties in a museum of palæontology. The monograph of the oceanic hydrozoa, although published in 1859, had been completed long before. Two papers, which continue work begun on the Rattlesnake, are the memoir on Pyrosoma (Trans. Linn. Soc. 1859), and that on Aphis (1857). Each of these describes an alternation of generation, and so continues the early work on salpa : but with these exceptions the greater part of the work published between 1855 and 1859 deals either with fossil forms or with problems suggested by them. Among the more important of the descriptive memoirs (some twenty in number) published before the end of 1859, we must mention that on cephalaspis and pteraspis (1858), in which the truth of the suggestion that pteraspis is a fish is finally demonstrated ; the accounts of the eurypterina (1856-9) ; the descriptions of dicynodon, rhamphorhynchus, and other reptiles. These studies of fossils seem to have been carried on simultaneously with that of the living forms related to them; thus the work on fossil fishes (the main results of which were not published until 1862) was accompanied by a study of the development of skull and vertebral column in recent fishes (Quart. Journ. Micr. Sci. 1859), and by the histological work upon their exoskeleton published in Todd's 'Encyclopædia of Anatomy and Physiology' (article 'Tegumentary Organs'). The description of extinct crocodilia led to an investigation of the dermal skeleton in living genera (Journ. Linn. Soc. 1860). The most important problem, suggested by continual work upon vertebrates, whether recent or fossil, is that presented by the composition of the skull. The doctrine prevalent in England was that which Owen had learned from Goethe and Oken. According to Owen, the archetype skeleton of a vertebrate 'represents the idea of a series of essentially similar segments succeeding each other in the axis of the body ; such segments being composed of parts similar in number and arrangement.' Attempts were made, in accordance with this theory, to divide the skull into a series of rings, each of which was supposed to contain every element present in a post-cranial vertebra. The result was a method of description which obscured the actual anatomical relations of the parts described ; and the attempt to demonstrate an archetypal idea by anatomical methods reached its climax of absurdity. Huxley applied to the skull the same method of analysis as that he had so successfully applied to other structures. In his essay 'On the Theory of the Vertebrate Skull,' read as the Croonian lecture before the Royal Society in 1858, he endeavours to formulate a morphological type of cranial structure in an inductive statement of those characters which are common to the skulls of a number of representative vertebrates in the adult and embryonic conditions. The lecture is based partly on the embryological work of Reichert, Rathke, and Remak, supplemented by observations of his own upon fishes and amphibia ; partly on a careful study of adult skulls. The result is a statement of cranial structure which has been justified in all essential points by the work of the last forty years. The lecture on the skull is admirable not only in substance but in form. The character of the audience justified the free use of such aid to concise statement as technical terms afford ; but when this is remembered the lecture must be regarded as a masterpiece of concise and lucid exposition, worthy to rank with the most brilliantly successful efforts of Huxley's later years.

For Huxley, as for many others, the most important event of 1859 was the publication of the 'Origin of Species.' He had maintained a sceptical attitude towards all previous hypotheses which involved the transmutation of species, and, in the chapter written for Mr. Francis Darwin's 'Life and Letters of Charles Darwin,' he says : 'I took my stand upon two grounds : firstly, that up