X PREFACE. 



As I have thus been obliged to speak of many things of which 

 I have no proper knowledge each section must inevitably seem 

 meagre to those who have made its subject their special study, 

 and I fear that many mistakes must have been made. To any one 

 who may be willing to help to set these errors right, I offer thanks 

 in advance, " humbly acknowledging a work of such concern- 

 ment unto truth did well deserve the conjunction of many heads." 



In the course of the work I have had help from so many that 

 I cannot here give separate thanks to each. For valuable criticisms, 

 given especially in connexion with the introductory pages, I am 

 indebted to Mr F. Darwin, Dr C. S. Sherrington, Dr D. MacAlister, 

 Mr W. Heape, Mr G. F. Stout, Dr A. A. Kanthack and particularly 

 to Mr J. J. Lister. I have to thank the authorities of the 

 British Museum, of the Museum of the Royal College of Surgeons, 

 of the Musee d'Histoire Naturelle in Paris, and of the Museums 

 of Leyden, Oxford, Rouen, Newcastle-upon-Tyne, of the Ecole 

 Ve'terinaire at Alfort, and of the Dental Hospital for the great 

 kindness that they have shewn me in granting facilities for the 

 study of their collections. In particular I must thank Mr Oldrleld 

 Thomas of the British Museum for much help and advice in con- 

 nexion with the subject of Teeth. I am also greatly obliged to 

 Messrs Godman and Salvin for opportunities of examining and 

 drawing specimens in their collections. To many others who have 

 been good enough to lend specimens or to advise in particular 

 cases my obligations are acknowledged in the text, but I must 

 especially express my gratitude to Dr Kraatz of Berlin, to Dr L. 

 von Heyden of Frankfurt, and to M. H. Gadeau de Kerville of 

 Rouen for the large numbers of valuable insects with which they 

 entrusted me. 



My best thanks are due to Dr A. M. Norman for many useful 

 suggestions, for the loan of specimens and for the kindly interest 

 he has taken in my work. 



My friend Mr H. H. Brindley has very kindly given me much 

 assistance in determining and verifying several points that have 

 arisen, and I am particularly indebted to him for permission to 

 give an account of his very interesting and as yet unpublished 

 observations on the variation and regeneration of the tarsus in 

 Cockroaches. 



Through the help of Dr David Sharp I have been enabled to 

 introduce much valuable evidence relating to Insects, a subject of 



