References to Harvey's finished writings will be made to two editions, viz.: The Works of William Harvey, translated from the Latin with a life of the author by R. Willis, M.D., London, 1847, printed for the Sydenham Society, which will here be designated as "Syd."; and Guilielmi Harveii Opera Omnia: A Collegio Medicorum Londinensi Edita: 1766, which will be designated as "Op. Omn." In the preparation of the text the present writer has used these two editions and also the first editions of Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, Frankfort, 1628, and Exercitationes de Generatione Animalium, London, 1651. Willis's translation of passages has been revised, often freely, where the writer has judged this desirable; and sometimes the revision amounts to a fresh translation. References to Harvey's lecture notes will be made to Prelectiones Anatomiæ Universalis by William Harvey, edited with an autotype reproduction of the original by a committee of the Royal College of Physicians, London, 1886. References to Galen's writings will be made to two editions, viz.: Claudii Galeni Opera Omnia. Editionem curavit C. G. Kühn, Leipsic, 1821-1833, which will be designated by the letters "Kn."; and Œuvres Anatomiques, Physiologíques et Medicáles de Galien, Traduites avec Notes par C. Daremberg, Paris, 1854-1856, which will be cited as "Dar." The former is the recognized working edition of the Greek text of Galen; this is accompanied by a Latin translation, to which is appended a serviceable Latin index. By the pages of this edition the Greek text of Galen is commonly cited. None of the treatises of Galen has been translated into English. Some of those most interesting to physiologists may be read in the above French translation of Daremberg. A critical edition of the Greek text of Galen's treatise On the Doctrines of Hippocrates and Plato, Claudii Galeni de Placitis Hippocratis et Platonis, with an amended Latin translation by Johannes Müller, was published by Teubner, Leipsic, 1874; it will here be cited as "Mül." References to Aristotle's writings will be made to Aristotelis Opera: Edidit Academia Regia Borussica, Berlin, 1831-1870, which is the commonly cited Greek text. Pages and lines of this edition will always be found in the margin of a modern edition or translation. The following works of Aristotle will be referred to in this paper:-- The Psychology and its appendices, viz.: the so-called "Lesser Works on Natural Things (Parva Naturalia)." English translation by W. A. Hammond, New York, 1902. The two last treatises of the Parva Naturalia have also been translated by W. Ogle, M.D., London, 1897. The History of Animals. English translation by R. Creswell. Bohn's Classical Library. London, 1878. On the Parts of Animals. English translation by W. Ogle, M.D., London, 1882.