PKEFACE TO VOL. II. 



THE proof sheets of this volume, like those of the last 

 volume, have been looked through by Dr. Hooker and 

 Prof. Huxley ; and I have, as before, to thank them for 

 their valuable criticisms, and for the trouble they have 

 taken in checking the numerous statements of fact on 

 which the arguments proceed. The consciousness that 

 their many duties render time extremely precious to them, 

 makes me feel how heavy is my obligation. 



Part IV., with which this volume commences, contains 

 numerous figures. Nearly one half of them are repeti 

 tions, mostly altered in scale and simplified in execution, of 

 figures, or parts of figures, contained in the works of vari 

 ous Botanists and Zoologists. Among the authors whom I 

 have laid under contribution, I may name Berkeley, Car 

 penter, Cuvier, Green, Harvey, Hooker, Huxley, Milne- 

 Edwards, Ralfs, Smith. The remaining figures, numbering 

 150, are from original sketches and diagrams. 



The successive instalments w^hich compose this volume, 

 were issued to the Subscribers at the following dates : No. 

 13 (pp. 180) in January, 1865 ; No. 14 (pp. 81160) in 

 June, 1865 ; No. 15 (pp. 161 240) in December, 1865 ; No. 

 16 (pp. 241320) in June, 1866 ; No. 17 (pp. 321400) in 

 November, 1866 ; and No. 18 (pp. 401566) in March, 1867. 



LONDON, March 23rd, 1867. 



ix 



