PREFACE. 



That edition, with no more delay than circumstances 

 have rendered necessary, is now laid before the public. 

 It comprises four volumes. 



The first volume contains, in chronological order, 

 all Balfour's scattered original papers, including those 

 published by him in conjunction with his pupils, as well 

 as the Monograph on the Elasmobranch Fishes. The 

 last memoir in the volume, that on the Anatomy and 

 Development of Peripatus Capensis, was published after 

 his death, from his notes and drawings, with additions 

 by Prof. Moseley and Mr Adam Sedgwick, who prepared 

 the manuscript for publication. To the volume is pre- 

 fixed an introductory biographical notice. 



The second and third volumes are the two volumes of 

 the Comparative Embryology reprinted from the original 

 edition without alteration, save the correction of obvious 

 misprints and omissions. 



The fourth volume contains the plates illustrating the 

 memoirs contained in Vol. I. We believe that we are 

 consulting the convenience of readers in adopting this 

 plan, rather than in distributing the plates among the 

 memoirs to which they belong. To assist the reader the 

 explanations of these plates have been given twice : at 

 the end of the memoir to which they belong (in the 

 case of the Monograph on Elasmobranch Fishes at the 

 end of each separate chapter), and in the volume of 

 plates. 



All the figures of these plates had to be redrawn on 

 the stone, and our best thanks are due to the Cambridge 

 Scientific Instrument Company for the pains which they 

 have taken in executing this work. We are also indebted 

 to the Committee of Publication of the Zoological Society 

 for the gift of electrotypes of the wood-cuts illustrating 

 memoir no. xx. of Vol. i. 



