Jenkinson, John Wilfred

(b. London, England, 31 December 1871; d. Gallipoli, Turkey, 4 June 1915)

comparative embryology, experimental embryology.

A pioneering experimental embryologist in England in the first part of this century, Jenkinson, through his researches and teaching, stimulated interest in what was then a relatively new field of developmental biology. He was the second son of William Wilberforce Jenkinson, a surveyor, and the former Alice Leigh Bedale. As a schoolboy at Bradfield College he was an avid botanist, and his records of a number of the plants to be seen near Bradfield were cited in George Claridge Druce’s Flora of Berkshire (1897), which mentions a catalog that Jenkinson had made of the plants found in that vicinity.

When Jenkinson matriculated at Exeter College, Oxford, in 1890, it was with a classical scholarship; and during the next several years his studies centered on the classics, in which he attained honors, receiving his degree in Litterae humaniores. But he had managed to hear some lectures in biology; and in 1894 he turned to zoological studies with characteristic enthusiasm, entering University College, London, and gaining the necessary scientific background under the guidance of W. F. R. Weldon.

In zoology Jenkinson was drawn to embryology, and his study of normal comparative developmental biology led to an interest in experimental embryology. He was soon engaged in original investigation as he faced the difficulties involved in understanding growth and the causes of differentiation. Several stays in the Utrecht laboratory of the embryologist A. A. W. Hubrecht during vacation periods afforded Jenkinson further direction and facilities for researches which were published in 1900 in his first paper, on the early embryology of the mouse.

He returned to Oxford to assist in the teaching of comparative anatomy and embryology . In 1905 lie added the D .Sc. (Oxon .) to the M .A. and was married to Constance Stephenson . The next year he was named university lecturer in comparative and experimental embryology, and Exeter College elected him a research fellow in 1909 . But the course of his researches was not to be completed . With the Outbreak of World War I he volunteered for service ; sent to the Dardanelles, lie was killed within days at Gallipoli.

His classical studies had given Jenkinson a broad perspective in his approach to the problems of the biologist. He particularly examined the concepts of vitalism from the Aristotelian to those of Driesch, whose neovitalism he strongly contested. Repeatedly, in his writings and lectures, he returned to the issue of vitalism, while in his own researches he experimented to clarify some of the conditions, both internal and external, determining embryological development. Both as a scientist and as a philosopher Jenkinson examined the premises on which his experimentation was based, convinced that the processes of growth and change so remarkably evident during embryogeny bore investigation and that it was possible to isolate physical and chemical factors that interacted and influenced the mechanics of development.

Among the subjects of Jenkinson’s studies was the development of the mammalian placenta. Over several years, too, he sought to determine the relationship between the symmetry of the egg and that of the embryo in the frog. In his continuing investigations of the factors affecting the plane of symmetry, he realized their complexity; he demonstrated that in certain forms light and gravity might play some role. Jenkinson experimented to define the effects of various chemical agents upon the development of the embryo; using different isotonic solutions, he found that in some cases segmentation, gastrulation, or the course of formation of the medullary folds was affected, and chemical environmental factors were shown to change the rate or affect the normalcy of development.

To his contemporaries Jenkinson’s work was a reference point. His texts on experimental embryology (1909) and vertebrate embryology (1913) were compendiums and are of interest for their discussions of vitalism. They present some of the views of the day on embryology and on the germ cells. Jenkinson himself, for example, considered that the nucleus played only a limited role in inheritance; he thought the chromosomes were concerned with the transmission of generic, varietal, or individual characters; he assigned the larger part in heredity to cytoplasmic factors in the ovum. His papers in Archiv für Entwicklungsmechanik der Organismen, Biometrika, and other journals focused attention on the problems of the embryologist.

BIBLIOGRAPHY

I. Original Works. Among Jenkinson’s articles, defining some of the questions confronting embryology and describing his own work, are “Remarks on the Germinal Layers of Vertebrates and on the Significance of Germinal Layers in General,” in Memoirs and Proceedings of the Manchester Literary and Philosophical Society, 50 (1906), 1-89;“On the Effect of Certain Solutions Upon the Development of the Frog” Egg,” in Archiv fü Entwicklungsmechanic der Organismen, 21 (1906), 367-460;“On the Relation Between the Symmetry of the Egg, the Symmetry of Segmentation, and the Symmetry of the Embryo in the Frog,” in Biometrika, 7 (1909), 148-209, one of several communications on the subject over several years”work and “On the Effects of Certain Isotonic Solutions on the Development of the Frog,” in Archiv für Entwicklungs-mechanik der Organismen, 32 (1911), 688-699. In vertebrate morphology his papers include“The Development of the Ear-Bones in the Mouse,” in Journal of Anatomy and Physiology,45 (1911), 305-318. Many of Jenkinson’ observations and experimental results appear in his Experimental Embryology (Oxford, 1909) and Vertebrate Embryology (Oxford, 1913). Three Lectures on Experimental Embryology (Oxford, 1917) appeared posthumously His views on vitalism are published as a separate essay,“Vitalism,” in Charles Singer, ed., Studies in the History and Method of Science,I (Oxford, 1917), 59-78, and in Hibbert Journal, 9 (1911), 545-559; see also his essay,““Science and Metaphysics,”in Studies . . ., II (1921), 447-471.

II. Secondary Literature. Singer provides a biography and a bibliography in Studies . . ., I , 57-58. A biographical note by R. R. Marett prefaces Jenkinson’s Three Lectures, pp. xi-xvi. Obituary notices are “Dr. J. W. Jenkinson,”in Nature, 95 (1915), 456;and “Captain J. W. Jenkinson, M.A., D.Sc.,” in Proceedings of the Royal Society, 89B (1917), xlii-xliii.

Gloria Robinson