PREFACE 



THIS volume is the outcome of a course of lectures, delivered at 

 Columbia University in the winter of 1892-93, in which I endeavoured 

 to give to an audience of general university students some account 

 of recent advances in cellular biology, and more especially to trace 

 the steps by which the problems of evolution have been reduced to 

 problems of the cell. It was my first intention to publish these 

 lectures in a simple and general form, in the hope of showing to 

 wider circles how the varied and apparently heterogeneous cell- 

 researches of the past twenty years have grown together in a 

 coherent group, at the heart of which are a few elementary phe- 

 nomena, and how these phenomena, easily intelligible even to those 

 having no special knowledge of the subject, are related to the 

 problems of development. Such a treatment was facilitated by 

 the appearance, in 1893, of Oscar Hertwig's invaluable book on 

 the cell, which brought together, in a form well designed for the 

 use of special students, many of the more important results of 

 modern cell-research. I am glad to acknowledge my debt to Hert- 

 wig's book ; but it is proper to state that the present volume was 

 fully sketched in its main outlines at the time the Zelle und Gewebe 

 appeared. Its completion was, however, long delayed by investiga- 

 tions which I undertook in order to re-examine the history of the 

 centrosomes in the fertilization of the egg, a subject which had 

 been thrown into such confusion by Fol's extraordinary account of 

 the " Quadrille of Centres " in echinoderms that it seemed for a time 

 impossible to form any definite conception of the cell in its relation 

 to inheritance. By a fortunate coincidence the same task was inde- 

 pendently undertaken, nearly at the same time, by several other 

 investigators. The concordant results of these researches led to a 

 decisive overthrow of Fol's conclusions, and the way was thus cleared 

 for a return to the earlier and juster views founded by Hertwig, 

 Strasburger, and Van Beneden, and so lucidly and forcibly developed 

 by Boveri. 



The rapid advance of discovery in the mean time has made it 

 seem desirable to amplify the original plan of the work, in order to 

 render it useful to students as well as to more general readers ; and 

 to this end it has been found necessary to go over a considerable 



