PREFACE. ix 



Mr. A. Johnstone, F.G.S, (of the University of Edinburgh) ; 

 Dr. C. A. MacMunn, F.C.S. ; Prof. P. Mantegazza (of the 

 University of Eome) ; Dr. A. C. May bury, F.G.S. ; Prof. 

 A. von Mojsisovics (of the University of Gratz) ; Mr. E. B. 

 Poulton, F.R.S. ; Dr. G. J. Romanes, F.R.S. ; Prof. G. 0. 

 Sars (of the University of Christiania) ; and Dr. C. Zeiss, for 

 vahiable assistance in various parts of the book. • 



My obligations are due to the President and Council of 

 the Royal Society of Edinburgh for the loan of certain 

 wood-blocks used in illustrating my own papers on the 

 Invertcbrata, and which were originally printed in the 

 Society's Proceedings. 



In conclusion, I here record the name of my sister (Miss 

 Mildred H. Griffiths), for her help in preparing, under my 

 direction, certain drawings for the illustrations. Figures 32 

 and 33 are supplied by Dr. Carl Zeiss, optician, Jena, from 

 his catalogue of microscopes. 



A. B. GRIFFITHS. 



Edgbastok, Feb. 1892. 



