iv PREFACE 



It will be readily recognized that the present volume comprises 

 a selected sample, rather than a more comprehensive coverage 

 of investigations into problems of the initial developmental 

 changes undergone by the egg and early embryo. The investi- 

 gations presented in the various communications cover both de- 

 scriptive and experimental work on the biological and chemical 

 levels. Many of the articles contain results of previously unpub- 

 lished researches as well as general reviews of the particular 

 subject. 



No special attempt was made to force the contributions into 

 a preconceived plan, or to develop an overall general concept. 

 The interrelationships of the individual topics assured a reason- 

 able amount of unity to the work. In addition, there was exchange 

 of articles among some of the contributors, besides the verbal 

 discussions at the symposium, that provided opportunity for fur- 

 ther integration and for elimination of unnecessary repetition. 

 The instances of overlapping that remain were considered desir- 

 able, especially where there were differences in outlook and 

 interpretation. Although such differences reflect, in part, varia- 

 tions in point of view and judgment of the individual contribu- 

 tors, they serve mainly to emphasize the lack of critical informa- 

 tion concerning the particular problem under discussion. In fact 

 we consider much of the value of a work such as this to reside 

 in the extent to which it brings to the attention of students and 

 investigators these regions of uncertainty and indicates the kinds 

 of problems that are in urgent need of solution, along with the 

 modern methods by which answers may be sought. 



Apart from their intrinsic interest and the measure of progress 

 that they provide, the specific discoveries and analyses presented 

 in this book serve, then, to exemplify various approaches toward 

 our understanding of the manner in which sperm and egg con- 

 trive to produce a new individual. 



Albert Tyler 



