406 



NATURE 



[August 24, 1882 



or two places finds expression in words telling us that man 

 differs from the animal creation, if not in phy.Mcal characteristics 

 which cannot be bridged over, at least in moral attributes and in 

 the "ennobling belief in God," by his power of forming that 

 conception of the Deity which, to use Darwin's own words, is, 

 " the grand idea of God hating sin and loving righteousness." 

 ("The Descent of Man and Selection in Relation to Sex." 

 Second edition (1874), page 144.) 



We cannot help mourning for our great ones, though they be 

 taken from us in the fulness of years, and when their labours 

 have been so numerous and so productive that we marvel that 

 they have been able to achieve so much within the span of a 

 single life ; but our grief is immeasurably greater when the man 

 of genius is taken from us in the plentitude of strength, as 

 it were upon the threshold of a life full of extraordinary 

 promise. 



Francis Maitland Balfour, whose sudden death has so recently 

 cast a gloom over us all, was a man who appeared destined to 

 advance our knowledge of animal development more than it had 

 been advanced by the labours of any one of his predecessors. 

 His death recalls the train of thought which we have pursued 

 when reflecting upon the lives and works of such men as Mayow 

 and Bichat, Gerhardt and Clifford. If so much could be achieved 

 in so short a life, what great benefits would science not have 

 derived, what remarkable steps in advance might not have been 

 made, had it been given to these great minds to work on for the 

 good of their race during a lifetime of ordinary length. It must 

 be sufficient for us that it was destined otherwise ; and, in 

 mourning for our departed friend, we may at least reflect that 

 we would not have him less worthy of our admiration in order 

 that we might mourn him the less. 



The Researches of Francis Maitland Balfour. 



At the risk of having to be somewhat brief in my discussion of 

 the subject proper of this address, I must yield to the impulse 

 which leads me to give you some account of Balfour's work. 1 



Having been educated at Harrow, Balfour entered Trinity 

 College, Cambridge, in the year 1870. His friend and master, 

 Michael Foster has told us how, from the very first, besides 

 ■engaging in systematic studies which he was able to pursue with 

 no small degree of success, he devoted himself with passion 

 to original research. At the very outset Balfour engaged in 

 work which led to speculations of a fundamental and far-seeking 

 nature, and of the three embryological papers, (Studies from the 

 Cambridge Physiological Laboratory. Parti., 1873. Quarterly 

 Journal of Microsopical Science, vol. xiii., 1S73.) which he wrute 

 before taking his degree, two related to questions which occup ; ed 

 his attention in a special manner to the end. One of these, " On 

 the Development and Growth of the Layers of the Blastoderm," 

 ■contains several statements not afterwards maintained ; for in- 

 stance, as to the independent origin of the mesoblast in the 

 chick, where it is said "neither to originate from the epiblast 

 nor from the hypoblast, but to be formed coincidentally with the 

 latter, out of apparently similar segmentation cells." The other, 

 "On the Disappearance of the Primitive Groove in the Chick," 

 calls attention to, and corroborates Dttrsy's discovery of seven 

 years before, and closes with a suggestion of the great hypothesis 

 (afterwards elaborated) that the primitive streak is a lingering 

 remnant of the blastopore. Balfour also w rote whilst an under- 

 graduate " On the Development of the Bloodvessels in the 

 Chick," but it may be doubted whether he advanced our 

 knowledge of this obscure subject. 



The " Elements of Embr)ology," by Michael Foster and 

 Balfour, appeared (1874) shortly after Balfour had taken his 

 ■degree (1S73), anc ^ Foster has generously recorded how great was 

 the part his pupil took in the production of this book. The 

 month after taking his degree he made his first journey to Naples, 

 and it was whilst working there that he entered upon bis remark- 

 able investigation on the development of Elasmobranchs. The 

 natural outcome of Gegenbauer's exposition (Gegenbauer, " I'as 

 Kopfskelett der Selachier," 1872) of the pi imitive character of 

 this group was that increased interest shtuld attach to all re- 

 searches on its embryology. To an introductory account of the 

 embryology of Elasmobranchs (Quarterly Journal oJ Microscop- 

 ical Science, vol. xiv., 1S74. ) Balfour owed, I believe, his fellow- 

 ship at Trinity College, and from that time onwards until 187S 

 he pursued the investigation at Naples and in Cambridge. The 



1 In the preparalion of this part of my address I have been very greatly 

 -aided by one of Balfour's pupils, my nephew, D'Arcy \V. Thompson, 

 Scholar of Trinity College. 



collected results appeared in 1878, as "A Monograph on the 

 Development of Elasmobranch Fishes." No research upon a 

 limited group ever contained more numerous or more wide 

 generalisations, extending over the whole domain of vertebrate 

 embryology. I may dwell for a few moments upon some of its 

 most interesting sections. 



The structures which we are now familiar with as "head- 

 cavities " are described for the first time, and named ; their 

 relation to thecranial nerves and their resemblance or equivalence 

 to the muscle plates of the body are pointed out ; and Balfour 

 seizes upon their value in throwing light upon the great problems 

 of the segmentation of the head and the segmental value of the 

 cranial nerves. In particular the 5th nerve and the 7th, v. ith the 

 auditory, are specified as the segmental nerves of the mandibular 

 and hyoid segments. The short, but very important, notice of 

 the sympathetic system showed that its ganglia developed on 

 branches of the spinal nerve, and that it was therefore a product 

 of the epiblast (" Elasmobranch Fishes," p. 172.) The primitive 

 features of the mesoblast and notocord and their hypoblastic 

 origin are described, ("Elasmobranch Fishes," pp. 49, S5, 92, 

 104.) and furnish material for the comparison afterwards institu- 

 ted in the " Comparative Embryology" (vol. ii., pp. 243, 246.) 

 between their development in Elasmobranchs and their still more 

 primitive origin in Amphioxus, as diverticula of the archenteron. 

 A very able chapter on excretory organs concludes this monograph. 

 This subject had engaged Balfour's attention very early, and bis 

 introductory account of Elasmobranch Development contains his 

 discovery of segmental organs in Elasmobranchs, — a discovery 

 made independently but simultaneously by Professor Semper. 

 These organs are shown to develop in the mesoblast, and are 

 compared with the segmental organs of annelids. 



A paper published in 1876 gives a singularly clear and thorough 

 re's um e of our knowledge of the development of the urino-genital 

 system ; and the diagrams there given, illustrating the homologies 

 of the male and female urino-genital organs, are wonderfully 

 simple and instructive. Shortly after the publication of this 

 paper, Balfour became a Fellow of the Royal Society, for which 

 he received a Royal Medal in 1881. 



Among the intere.-ting points that Balfrur had made clear in 

 connection with the spinal nerves of Elasmobranchs, was the 

 fact that the anterior and posterior roots arise alternately, and 

 not in the same vertical plane. He sought for an explanation of 

 this in Amphioxus at Naples, in 1876. Owsjannikow and Stieda 

 had discovered that the nerves of the opposite sides in Amphioxus 

 arise alternately, and Stieda further stated that the nerves of the 

 same side arise alternately from the dorsal and ventral corners of 

 the cord. Stieda considered that two adjacent nerves were 

 together equivalent to a single spinal nerve of higher vertebrates. 

 Balfour (Journal of Anatomy and Physiology, vol. x., 1876.) 

 found no trace of difference of level in the origin of nerves on 

 the same side, i.e. he denied the existence of ventral or anterior 

 roots ; and afterwards, in investigating the cranial nerves of 

 higher vertebrates, and being unable to find any trace of anterior 

 roots, he framed the bold hypothesis (" Elasmobranch Fishes," 

 P- '93' "Comparative Embryology," vol. ii., p. 380.) that the 

 head and tiunk had been differentiated from each other at a lime 

 when mixed motor and sensory posterior roots were the only 

 roots present, and that cranial and spinal nerves had been inde- 

 pendently evolved from a common ground-plan. 



Balfour's investigation of the development of the ovary was 

 incomplete when his work on Elasmobranchs appeared ; and he 

 continued to work at this subject, both in Elasmobranchs and 

 Mammals, publishing upon it in 1S78 (Quarterly 'Journal of 

 Microscopical Science, vol. xviii., 187S.) A paper published in 

 the same year, on the "Maturation and Impregnation of the 

 Ovum," contained the very ingenious suggestion ihat the casting 

 out of the polar bodies prevents the ovum developing by itself 

 into a new individual, i.e. prevents parthenogenesis ; and Balfour 

 points out that parthenogenesis is practically confined to the 

 arthropoda and rotifera, which are the only two groups in which 

 polar bodies are not known to occur. 



Balfour still continued, now in conjunction with Sedgwick, his 

 researches on the urino-genital system, and described, among 

 many other new points, the existence of a head-kidney 

 (pronephros) in the chick (Proceedings of the Royal Society, vol. 

 xxvii., 1878). 



In this year, Balfour also investigated (Quarterly Journal 0/ 

 Microscopical Science, vol. xix., 1S79.) the early development of 

 Lacerta, and pointed out ihe presence of a primitive streak and 

 of a neurenteric canal. This investigation confirmed his belief 



