vi PREFATORY NOTE 



To the Council of the Royal Society of Edinburgh, and to that 

 of the Zoological Society of London : — the former for letting me 

 reprint from their Transactions the greater part of the text and 

 illustrations of my concluding chapter, the latter for the use of a 

 number of figures for my chapter on Horns. 



To Professor E. B. Wilson, for his well-known and all but 

 indispensable figures of the cell (figs. 42 — 51, 53) ; to M. A. Prenant, 

 for other figures (41, 48) in the same chapter; to Sir Donald 

 MacAhster and Mr Edwin Arnold for certain figures (335 — 7), 

 and to Sir Edward Schafer and Messrs Longmans for another (334), 

 illustrating the minute trabecular structure of bone. To Mr 

 Gerhard Heilmann, of Copenhagen, for his beautiful diagrams 

 (figs. 388-93, 401, 402) included in my last chapter. To Pro- 

 fessor Claxton Fidler and to Messrs Grifl&n, for letting me use, 

 with more or less modification or simplification, a number of 

 illustrations (figs. 339 — 346) from Professor Fidler's Textbook of 

 Bridge Construction. To Messrs Blackwood and Sons, for several 

 cuts (figs. 127 — 9, 131, 173) from Professor Alleyne Nicholson's 

 Palaeontology ; to Mr Heinemann, for certain figures (57, 122, 123, 

 205) from Dr Stephane Leduc's Mechanism of Life ; to Mr A. M. 

 Worthington and to Messrs Longmans, for figures (71, 75) from 

 A Study of Splashes, and to Mr C. R. Darhng and to Messrs E. 

 and S. Spon for those (fig. 85) from Mr Darhng's Liquid Drops 

 and Globules. To Messrs Macmillan and Co. for two figures 

 (304, 305) from Zittel's Palaeontology; to the Oxford University 

 Press for a diagram (fig. 28) from Mr J. W. Jenkinson's Experi- 

 mental Embryology; and to the Cambridge University Press for 

 a number of figures from Professor Henry Woods's Invertebrate 

 Palaeontology , for oife (fig. 210) from Dr Willey's Zoological Results, 

 and for another (fig. 321) from " Thomson and Tait." 



Many more, and by much the greater part of my diagrams, 

 I owe to the untiring help of Dr Doris L. Mackinnon, D.Sc, and 

 of Miss Helen Ogilvie, M.A., B.Sc, of this College. 



D'ARCY WENTWORTH THOMPSON. 



University College, Dundee. 

 December, 1916. 



