John Wilfred Jenkinson was born in 1871, and came from Bradfield to Exeter College, Oxford, with a classical scholarship in 1890. After taking his degree in _Literae Humaniores_ he came, in 1894, to University College, London, where he devoted himself with extraordinary and never-flagging energy to biological studies. Without having had the usual preliminary scientific teaching, he brought, on the other hand, a well-trained mind to bear on his new work, and the rapidity and completeness with which he acquired his scientific equipment was one of the most striking and interesting points in his career. Jenkinson very soon turned to original investigation, and from the first he showed a predilection for Embryology. For a short time he held a post at one of the great London hospitals, but he soon returned to Oxford to join the teaching staff of the Department of Comparative Anatomy. He used the opportunity of University vacations to work in the laboratory of the late Professor A. A. W. Hubrecht at Utrecht, where part of his first published research was written. During the fifteen years of life that remained to him, he established himself as the foremost English writer on Embryology, devoting himself especially to its experimental aspect, a line of work in which he will rank as one of the pioneers. Jenkinson became Doctor of Science in 1905, and in the same year he married Constance Stephenson. In 1906 he was appointed University Lecturer in Embryology, and in 1909 he was elected to a Research Fellowship at Exeter College. Jenkinson’s mind was not of the type that matures early, but one felt in him a power of solid intellect that gained in force from year to year. The gap in the ranks of British Science caused by his death has been generally recognized, but his loss seems greatest to those personally acquainted with him, who know that he had by no means reached the zenith of his powers. Jenkinson led a single-minded and unselfish life, wholly free from worldly and ignoble ambitions. Of simple and winning humour, happy in his domestic life and absorbed in his studies, he represented the very best type of scientific worker. He was gifted with a powerful physique, and on the outbreak of war he became an ardent member of the Oxford Volunteer Training Corps. His qualities of calm courage and high sense of duty marked him out as a valuable officer. Although forty-three years of age, he took a commission in the 12th Worcester Regiment in January, 1915, and was promoted Captain in the following April. On May 10 he left for the Dardanelles, having been selected for service with the 2nd Royal Fusiliers. He was killed in action on June 4, only ten days after his arrival at the Gallipoli peninsula. BOOKS AND PAPERS BY J. W. JENKINSON 1. ‘A Re-investigation of the Early Stages of the Development of the Mouse.’ _Quart. Jour. Micr. Science_, xliii. 1900.