Balfour, Francis Maitland

(b. Edinburgh, Scotland, 10 November 1851; d. near Courmayeur, Switzerland, 19/20July 1882)

embryology.

The third son of James Maitland Balfour and Lady Blanche, daughter of the marquis of Salisbury, Francis Balfour came from an illustrious family, the outstanding member of which was his oldest brother, the prominent philosopher and statesman Arthur James Balfour. Francis spent his childhood at Whit–tingham. He attended the preparatory school at Hoddesdon, Hertfordshire, and in 1865 enrolled at Harrow. A keen naturalist as a boy, at Harrow Balfour wrote a prize–winning essay for the school’s scientific society, ’The Geology and Natural History of East Lothian,” which was judged and highly praised by Thomas H. Huxley.

Balfour matriculated at Trinity College, Cambridge, in 1870; he took a first in the Natural Science Scholarships the following year, and by 1872 was working under the direction of the physiologist Michael Foster. During the winter of 1873/1874 he began his investigation of the embryology of elasmobranchs at the Stazione Zoologica in Naples, work he pursued intermittently, both in Italy and in Cambridge, until 1878, when he completed his outstanding monograph on elasmobranch development. He began lecturing on morphology and embryology at Trinity College in the fall term of 1873 and became director of the university’s morphological laboratory, where he attracted an extraordinarily enthusiastic group of students. Balfour was elected to the Royal Society in 1878, became vice–president of the biological section of the British Association for the Advancement of Science in 1880, and won the Royal Society’s Royal Medal the following year upon completion of his two–volume text on comparative embryology.

Balfour’s star had risen so quickly and his reputation as a remarkable teacher was so well known that it was not surprising that both Oxford and the University of Edinburgh tried to lure him away from Cambridge. In 1882, at the urging of Foster, Cambridge created a professorship of animal morphology that Balfour was to hold for his lifetime; but before the year was out, Balfour was dead. For several years he had spent his vacations mountain climbing in Switzerland and had become an experienced alpinist. On 18 July 1882 he set out with his Swiss guide to scale the unconquered peak Aiguille Blanche de Peteret in the Chamonix district. They failed to return; their bodies were recovered at the foot of an icefall several days later.

Balfour’s embryological contributions exemplify the descriptive studies that characterized the two decades of embryology following the publication of Darwin’s Origin of Species. He began his research in Naples at a time when Ernst Haeckel, Aleksandr Kovalevski, E. Ray Lankester, and Anton Dohrn, among others, were emphasizing comparative embryology and placing a premium on the search for homologies and phylogenetic links. Balfour’s work was unquestionably directed by similar concerns, but his painstaking microscopic examinations and his crisp ordering of embryological details permitted him to draw certain sound generalizations about development that are far more impressive to the historian than the wilder speculations of his peers.

His monograph on elasmobranchs wasa closely knit document of nearly 300 pages. At the outset, Balfour avoided the customary phylogenetic discussion; instead, he began by describing the development of the ovum and the segmentation of the fertilized egg. He carried the description forward by embryonic stages until, at the end of the treatise, he could give a detailed analysis of the major organ systems and interpret their development in relation to that in other animals. Balfour’s analysis of germ–layer formation in elasmobranchs is a good example of his detailed microscopic examination and also demonstrates his ability to draw far–reaching generalizations. Carefully tracing the migration of lower–level cells during the formation of the segmentation cavity, he argued that both the segmentation cavity and the alimentary canal were formed by a delamination in the hypoblast. At first glance this conclusion had grave implications for Haeckel’s gastraea theory, to which Balfour himself subscribed, because Haeckel had maintained that the alimentary canal of all vertebrates was formed by an involution of the epiblast—that is, in the same manner that the archenteron of his hypothetical gartraea had been formed in eons past.

At this juncture Balfour introduced quite a different question; if the segmentation cavity and alimentary canal in amphioxus, elasmobranchs, amphibians, and birds were to be conisideres homologous, how should one interpret their different germ–layer origins? He concluded that one must take into consideration the quantity of yolk in the egg and its degree of segmentation at the time of germ–layer formation. Thus, he argued that since there was little yolk in amphioxus and amphilbian eggs, there existed perforce an anus of Rosconi and an involution of the epiblast at the dorsal lip of the blastopore; however, his argument continued, since there was a large quantity of yolk in elasmobranch eggs, there existed only a temporary anal opening and a delamination of the hypoblast. As for bird eggs, which held an extremely large quantity of yolk, Balfour claimed that no anus of Rosconi could possibly exist, not could the epiblast invaginate. In this explanation Balfour indicated an appreciation for the mechanical influences of cellular movement that forced different embryos to develop along different lines, irrespective of their phylogenetic connections.

Balfour’s recognition of the mechanical influence of the mass of yolk may have prompted his inquiry into the meaning of the primitive streak of the chick embryo. Comparing the positions of amphibian and selachian embryos which are asymmetrically situated on the blastoderm, with the chick embryo, which lies on the center, Balfour argued that the primitive streak was the homologue of the blastopore in the lower vertebrates. In collaboration with one of his students, Balfour further explained that the mesoblast of the chick was derived through a simultaneous differentiation from both the hypoblast and the epiblast, which lay along the axial line of the primitive streak. Such evidence again implicitly challenged a too rigid belief in the specificity of the germ layers. Balfour, however, did not draw the ultimate conclusions but faithfully adhered to the germ–layer doctrine.

In his study of elasmobranchs, Balfour included a detailed and superb description of the development of the excretory system. Although this work was anticipated in many respects by Karl Semper’s similar study, Balfour definitively pointed out the initial segmental character of the Wolffian duct (“segmental duct”) and traced the manner in which the Müllerian duct arose from the Wolffian duct’s ventral side. He then described in detail how the Müllerian duct in the female became converted to the oviduct and how the Wolffian duct in the male was utilized by the testes as the vas deferns. Considering the various modes of development in the abdominal opening of the Müllerian duct in elasmobranchs, amphibians, and birds, Balfour argued that there were sufficient differences to indicate three lines of urogenital evolution that diverged from a more general and primitive state. Although it is clear that the reconstruction of an evolutionary tree was a concern which constantly framed his detailed research. Balfour again minimized a discussion of the phylogenetic implications of his work.

When one surveys his many shorter articles, it is surprising to discover how strategically Balfour covered portions of the animal kingdom. A clear pattern emerges from his studies of elasmobranchs,Lepidosteus (a ganoid), amphioxus, Peripatus (an aberrant arthropod), and Araneina (a true spider), in which Balfour appears intent upon locating possible links between major taxa. Although he did not commit himself to any current theory concerning the link between invertebrates and vertebrates, he believed that any protochordate must have been segmental in character and must have had a suctorial mouth on the ventral surface. He believed, moreover, that any claimant of the title “missing link” must show undeniable signs of a primitive notochord.

Even taking these broader interests in phylogeny into consideration, it is still remarkable that within three years of the completion of his monograph on elasmobranchs, Balfour finished his two–volume Treatise on Comparative Embryology (1880–1881). According to Waldeyer, this was the first successful attempt at a complete comparative embryology text; it was translated into German the same year, and one finds important references to it for decades thereafter. Not only did Balfour survey developments peculiar to each phylum and give a comparative survey of the embryology of each organ system, but he also included introductory chapters on gamete formation, fertilization, and early cleavage, additions that demonstrated his keen interest in the most recent advances in cytology. By 1882 microscopy had made such rapid gains that many of Balfour’s facts, particularly about the nucleus, were already dated. There are certain signs, however, that he would have become more involved in this direction of research; in fact, as indicated above, there are even signs that he would have appreciated the type of question which the experimental embryologists in Germany began asking of the embryo from about 1882. Reflecting upon these interests, one can only muse how the embryological sciences in England would have progressed had Balfour not died at the age of thirty.

BIBLIOGRAPHY

The Works of Francis Matialnd Baldour, Michale Fosterand Adam Sedgwick, eds., 4 vols. (London, 1885), contains all of Balfour’s published works, including A Monograph on the Development of the Elasrnobranch Fishes (London, 1878) and A Treatise on Comparative Embryology, 2 vols. (London, 1880–1881).

There are only a few scanty biographical notices on Balfour, and even fewer discussions of his work. Besides Michael Foster’s introduction to the collected works, W. Waldeyer, “Frster’s Maitland Balfour, Fin Nachruf,’ in Archiv für mikroskopische Anatomie, 21 (1882), 828–835, and Henry Fairfield Osborn, “Francis Maitland Balfour,’ in Science, 2 (1883), 299–301, are useful. Balfour’s work is placed in its historical context in E. S. Russell, Form and Function, a Contribution to the History of Animal Morphology (London, 1916), pp. 268–301.

F. B. Churchill