PREFACE Vll 



student of embryology to evaluate the fruits of our common labors. 



Embryology is a basic subdivision of biology. From it stem the 

 anatomy, the histology, and the physiology of the adult. To under- 

 stand it well is to aid in the comprehension of the other biological 

 disciplines. 



To know one's self it is not sufficient to study the present-day 

 transiency. Such a study will be enhanced to the degree that it is sup- 

 ported by a knowledge of what preceded the present. To be a Jacques 

 Loeb and thus be qualified to make such a statement as "The most 

 uninteresting thing I know is the normal development of an egg," one 

 has first to know formal, basic, morphological embryology as thor- 

 oughly as it is possible to comprehend. It is only then that we can 

 appreciate and intelligendy apply the experimental method to the 

 problems of embryology. Possibly, were Loeb alive today, he would 

 be one of the first to admit that we know less about the normal de- 

 velopment of the frog than we thought we knew at the time of his 

 statement. Even for the ten-thousandth time, the formation of the 

 tension lines of the first cleavage furrow or the initial involution of the 

 gastrula are still among the most challenging of unsolved mysteries 

 both to the author and to his students. 



The adult "organism as a whole" is, in part at least, an expression 

 of its earlier experiences as an embryo. We may even have to admit 

 that the ultimate personality begins its realization at the moment of 

 fertilization. Certainly, to by-pass a study of the development of the 

 most rapid, the most dynamic, the most plastic stage of one's entire 

 physical existence is to miss the sum and substance of life itself. It 

 is the author's firm belief that anyone who completely understands 

 the mechanism of normal embryonic development will, to a com- 

 parable degree, understand life at any level. Further, in understand- 

 ing the embryology of the frog completely, one would come very close 

 to an understanding of the basic principles of development of any 

 form whatsoever. 



Roberts Rugh 



New York City, 

 June 1950. 



