The results of these early studies were made known in three papers which appeared in the _Quarterly Journal of Microscopical Science_ for July 1873, and will be found in the beginning of this volume. The summer and autumn of that year were spent partly in a visit to Finland, in company with his friend and old school-fellow Mr Arthur Evans, and partly in formal preparation for the approaching Tripos examination. Into this preparation Balfour threw himself with characteristic energy, and fully justified my having encouraged his spending so much of the preceding time in original research, not only by the rapidity with which he accumulated the stock of knowledge of various kinds necessary for the examination but also by the manner in which he acquitted himself at the trial itself. At that time the position of the candidates in the Natural Sciences Tripos was determined by the total number of marks, and Balfour was placed second, the first place being gained by H. Newell Martin of Christ's College, now Professor at Baltimore, U.S.A. In the examination, in which I took part, Balfour did not write much, and he had not yet learnt the art of putting his statements in the best possible form; he won his position chiefly by the firm thought and clear insight which was present in almost all his answers. The examination was over in the early days of Dec. 1873 and Balfour was now free to devote himself wholly to his original work. Happily, the University had not long before secured the use of two of the tables at the then recently founded Stazione Zoologica at Naples. And upon the nomination of the University, Balfour, about Christmas, started for Naples in company with his friend Mr A. G. Dew-Smith, also of Trinity College. The latter was about to carry on some physiological observations; Balfour had set himself to work out as completely as he could the embryology of Elasmobranch fishes, about which little was at that time known, but which, from the striking characters of the adult animals could not help proving of interest and importance. From his arrival there at Christmas 1873 until he left in June 1874, he worked assiduously, and with such success, that as the result of the half-year's work he had made a whole series of observations of the greatest importance. Of these perhaps the most striking were those on the development of the urogenital organs, on the neurenteric canal, on the development of the spinal nerves, on the formation of the layers and on the phenomena of segmentation, including a history of the behaviour of nuclei in cell division. He returned home laden with facts and views both novel and destined to influence largely the progress of embryology. In August of the same year he attended the meeting of the British Association for the Advancement of Science at Belfast; and the account he then gave of his researches formed one of the most important incidents at the Biological Section on that occasion.