vi PREFACE TO THE REVISED EDITION. 



oiatcd in the first edition are qualified and developed. 

 Various modern ideas are considered under the title " Ke- 

 cent Criticisms and Hypotheses." And the chapter on 

 " The Arguments from Embryology " has been mainly re- 

 written. Smaller increments have taken the shape of new 

 sections incorporated in pre-existing chapters. They are 

 distinguished by the following section-marks : 8#, 46a, 

 8fcz, 1000, 113a, 127a, 130a I30d. There 

 should also be mentioned a number of foot-notes of some 

 significance not present in preceding editions. Of the 

 three additional appendices the two longer ones have al- 

 ready seen the light in other shapes. 



After these chief changes have now to be named the 

 changes necessitated by revision. In making them assist- 

 ance has been needful. Though many of the amendments 

 have resulted from further thought and inquiry, a much 

 larger number have been consequent on criticisms received 

 from gentlemen whose aid I have been fortunate enough to 

 obtain : each of them having taken a division falling within 

 the range of his special studies. The part concerned with 

 Organic Chemistry and its derived subjects, has been looked 

 through by Mr. W. H. Perkin, Ph.D., F.R.S., Professor 

 of Organic Chemistry, Owens College, Manchester. Plant 

 Morphology and Physiology have been overseen by Mr. 

 A. G. Tansley, M.A., F.L.S., Assistant Professor of Bot- 

 any, University College, London. Criticisms upon parts 

 dealing with Animal Morphology, I owe to Mr. E. W. Mac- 

 Bride, M.A., Fellow of St. John's College, Cambridge, Pro- 

 fessor of Zoology in the McGill University, Montreal, and 

 Mr. J. T. Cunningham, M.A., late Fellow of University 



