558 KEPORT— 1882. 



entered Trinity College. At the brilliant Belfast meeting in 1874 he read his first 

 paper before the Association on Elasmobranch Fishes ; and this paper and Balfour's 

 share in the keen discussion which followed are still remembered with admiration 

 by many. In 1880, at Swansea, he delivered an address, as Chairman of the sub- 

 section of Anatomy and Physiology, deaUng with the mutual services rendered by 

 the evolution theory to erabryolog}', and by embryology to the evolution theory, 

 with special reference to the developmental history of the nervous system. In 

 1881, he was appointed one of the two General Secretaries. 



But the great text-book of comparative embryology '■ is the real monument 

 of Balfour's fame. It is impossible to com-ey an idea of the merits of this book. It 

 grappled with the enormous mass of scattered literature iipon the subject, and 

 formed it all into a consecutive account, clear and accurate. Discordant statements 

 .were weighed and estimated, frequently brought into harmony by an ingenious ex- 

 planation or by a new and crucial observation. Countless investigations were repeated 

 and verified, and countless suggestions of important work, that still remains to be 

 done, make the book as valuable to the savant as to the student. Among the 

 chapters ^ most remarkable for broad and philosophic generalisations are those deal- 

 ing with the ' Ancestral Form of the Ohordata,' ' Larval Forms,' and the ' Origin 

 and Homologies of the Germinal Layers.' Balfour accepts the gastrula as a stage 

 in the evolution of the metazoa, and leans somewhat to invagination, as the more 

 primitive process than delamination in the production of the gastrula. He shows 

 distinctly that the mesoblast arose in the first instance, not independently, but as a 

 differentiation from the other two layers, and that the mesoblast is a homologous 

 structure throughout the triploblastic metazoa. In the chapter on ' Larval Forms ' 

 he gives numerous reasons and arguments for a larval development repeating the 

 ancestral history, better and more fully than a foetal development ; he reviews the 

 types of larviB (discriminating six types), the causes tending to produce secondary 

 changes in larvte, and suggests, as a hypothesis for the passage from the radial to 

 the bilateral type, that in a pilidium-like larva the oral face elongated unequally, 

 an anterior part forming a pra3-oral lobe, and a posterior outgrowth the trunk, 

 while the aboral surface became the dorsal surface. He suggests that adult 

 Echinodermata have retained, and not secondarily acquired, their radial symmetry, 

 and considers a radially symmetrical organism, like a medusa, as the prototype of all 

 the larval forms above the coslenterates. Balfour does not admit the specially close 

 relationship of the Chordata with the Chretopods, which Dohrn and Semper main- 

 tain ; but considers that the Chordata descended from a stock of segmented worms 

 derived from the same unsegmented types as the Chmtopods, but in which two 

 lateral nerve-cords like those of the nemertines coalesced dorsally instead of ventrally. 

 He considers that the mouth in ancestral Cliordata was suctorial, and was not 

 formed, as Dohrn supposes, by the coalescence of two visceral clefts. Finally, 

 Balfour draws up a scheme of the phylogeny of the Chordata, according to which 

 the hypothetical protochordata, with a notochord, a suctorial mouth, and very 

 numerous gill-slits, acquired one by one, A'ertebrte, jaws, an air-bladder, a penta- 

 dactyl limb, an amnion : each new accession characterising a hypothetical proto- 

 group, from which some existing group is supposed to have diverged. 



Those of my hearers who had not followed Balfour's scientific labours, but who 

 merely knew him as one of the most respected workers in the field of biology, 

 will I trust, even from my brief sketch, have formed some idea of the activity and 

 originality of his mind, and will understand how his death has occasioned a feeling 

 almost akin to despair, in that he occupied a place which it appears to us now im- 

 possible to fill. ' How are the mighty fallen, and the weapons of war perished ! ' 



' Cnmparative Embryology, vol. i. 1880, vol. ii. 1881. 

 * Ibid. vol. ii. chaps, xi. xii. xiii. 



I 



