The two other of the three great treatises for anatomical students are the _Manual of the Anatomy of Vertebrated Animals_, published in 1871, and the _Manual of the Anatomy of Invertebrated Animals_, published in 1877. Of these two volumes it is sufficient to say that they formed the chief introduction to the study of animal zoölogy for many years, and that a large number of the best-known zoölogists of the end of this century received from them their first instruction in the science. As text-books they have been superseded lately by larger volumes in which there is found more space for some of the recent advances in knowledge, especially comparative embryology, and the more intricate knowledge of the structure of the soft parts of marine invertebrates made possible by the newer and more successful methods of preserving delicate tissues. Just before Huxley ceased his regular work as a teacher at the Royal College of Science, there arrived a series of marine embryos, beautifully preserved and prepared for microscopic work by the zoölogists at the International Zoölogical Station at Naples. Huxley is reported to have exclaimed at their beauty, and to have said: "You young men cannot realise your advantages; you have brought to you for study at your leisure in London, creatures that I had to lash my microscope to the mast to get a glimpse of." Huxley's books were written for students with fewer advantages, and, naturally, laid more stress on the harder skeletal parts and such structures as could be more easily preserved; but with this inevitable limitation they still serve as luminous and comprehensive guides to the subjects of which they treat. There is no doubt but that if he had been a younger man when the new technical methods made their appearance, he would have adopted them and their results in his volumes. One of the first great pieces of work which utilised methods more like those now used in all laboratories than those employed during the greater part of Huxley's life as a teacher was the classical investigation by Van Beneden into the changes in the egg of Ascaris which accompany the process of fertilisation. When Huxley read the memoir he exclaimed, "All this by the use of glacial acetic acid--is it possible!" At once, Professor Howes relates, he repeated the whole investigation himself, and, when satisfied, declared that the "history of the histological investigation of the future would be the history of its methods." Not only have the chemical substances used in preparing tissues for examination greatly increased since Huxley's time as an active worker, but a very important method of investigation has come into general use. In Huxley's time tissues or animals too large or too opaque to be examined microscopically as whole structures were either teased by needles or were cut with a razor by hand into comparatively thick slices. The process of cutting, however practised the operator, was