Pref 



rerace 



This book has been written for three reasons. First, since T. H. Mor- 

 gan's "Development of the Frog's Egg" (1897), there has been no 

 book written specifically on this subject. His was a most excellent 

 treatise, still remarkably accurate. Second, with the accelerated in- 

 terest in the experimental approach to the study of embryology, 

 stimulated by Spemann in Germany and Morgan and Harrison in 

 this country, and implemented by a host of their students, there 

 has been accumulated a large volume of information not available 

 in 1897. It is important that the description of normal embryology, 

 aided by this experimental approach, be brought up to date for the 

 frog. Third, with the discovery that the frog can be induced to 

 ovulate and provide living embryos at any time of the year, these 

 embryos have become one of the major test organisms in experimental 

 embryology. It is also being used increasingly in the related scientific 

 disciplines such as physiology, cytology, and genetics. 



The author disclaims any fundamental originality in this book. 

 All of the previous investigators and authors touching on the normal 

 embryology of the frog, from whose works much information has 

 been gathered, have been listed in the Bibliography. It is they who 

 have done much of the "spade work" for this book and the student 

 is encouraged to refer to these original sources. However, the author 

 has described the normal development of the frog to more than 5,000 

 students during 19 years of teaching, as a result of which an intimate 

 personal knowledge of all phases of frog embryology has inevitably 

 accrued. Further, the author organized one of the first laboratory 

 courses for experimental embryology in which the major experimental 

 form was the frog egg and embryo. From these two major lines of 

 work a personal interpretation of the development of the frog egg and 

 embryo has developed, built on the broad structural foundation laid 

 by a host of other workers. The author is responsible, however, for 

 any novelty of interpretation. 



The author has no intention of claiming any suggestion of final- 



