PART TL 



T. THE HISTORY OF THE EGG FROM FERTILIZATION TO 



CLEAVAGE. 



INTRODUCTION. 



It is now about fifteen years since the way was first cleared for a 

 better understanding of the processes known as maturation, impregna- 

 tion, and cleavage. We are chiefly indebted to the discoveries of Auer- 

 bach and Biitschli for the opening of this new era in cytological research, 

 which has already been prolific beyond precedent both in work and thought, 

 and promises to dwarf in importance everything that has preceded it. 



The problems presented go to the very foundations of life, and although 

 no one expects to reach a complete solution, the progress already made 

 encourages the hope that we may yet succeed in analyzing some of the 

 more subtile phenomena of life. 



The nematode egg has from the outset been a favorite object of study, 

 but the researches of Hertwig and Fol made the echinoderm egg the 

 chief centre of interest for a number of years. The brilliant studies of 

 Van Beneden sufficed to turn the tide of interest in favor of the ccq- of 

 Ascaris megabcepfmla, and for the last five or six years this egg has con- 

 tinued to lie the focal point of attention. We have now a voluminous 

 series of most interesting memoirs devoted to this single subject, repre- 

 senting the best efforts of such naturalists as E. Van Beneden, Nussbaum. 

 Schneider, Carnoy, Zacharias, and Boveri. But these most searching 

 analyses, beginning with Van Beneden and ending with Boveri, replete 

 with astonishing revelations and exhaustive almost beyond a parallel, 

 leave us at the beginning rather than at the end of this line of investi- 

 gation. Much more than has been done still remains to be accomplished 

 before we shall have a complete history of the remarkable phenomena 

 that form the prelude to development. 



