PREFACE 



, s its title is intended to indicate, the scope of this book 

 is not precisely that of a text-book. Generally speaking, 

 the purpose of a text-book, especially in a biological subject, 

 is to give a concise summary of the known facts, and per- 

 haps of established inferences from the facts, but not to 

 enter at any length into theoretical discussions, especially 

 when the leading investigators of the subject are not yet 

 in agreement upon their interpretation. The aim of this 

 book is rather different. While attempting to give an 

 account of the more important facts of animal cytology, its 

 chief purpose is to interest the student in the subject by 

 pointing out some of the ways in which cytological investi- 

 gation is related to the great fundamental problems that lie 

 at the root of all biological research. Some minds are 

 naturally interested in facts for their own sake, but to 

 these a rather specialised study like cytology is hardly 

 likely to make a strong appeal, and if, as the writer believes, 

 cytological investigation in the widest sense of the word 

 offers one of the most hopeful lines of advance in biological 

 knowledge, it seems essential that the bearing of cytological 

 facts on more general problems should be considered in any 

 introductory course on the subject. 



The plan of the book is based on that of the courses of 

 lectures given by the writer during some six years at Cam- 

 bridge. Those courses have naturally varied somewhat from 

 year to year; the subject has made very great advances 



