EARLY STAGES IN THE DEVELOPMENT OF THE 



CENTRAL NERVOUS SYSTEM OF 



AMBLYSTOMA PUNCTATUM 



LELAND GRIGGS 



From Dartmouth College, Hanover, N . H. 



TWELVE TEXT FIGURES AND ONE PLATE 



CONTENTS 



Introduction 425 



Historical review 426 



Definition of terms 437 



Material and methods 438 



Division into stages 441 



Description of embryos 442 



General conclusions 477 



Summary 479 



Bibliography 481 



Introduction 



The investigation of which this paper is an account was con- 

 ducted in the Zoological Laboratory of Dartmouth College 

 under the direction of Dr. William Patten. The method which 

 Dr. Patten used in his studies of the development of the ner- 

 vous system and sense organs of arthropods, an examination 

 of external markings of specially prepared embryos of a very 

 early stage, has been applied here to a study of these organs in 

 Amblystoma. I wish to express my indebtedness to Dr. Patten 

 for his suggestions upon my entering on the work and for his 

 careful supervision throughout. 



It is the purpose of this paper to offer a slight contribution 

 to the solution of the problem of vertebrate cephalogenesis. 

 The subject has been treated, however, in its narrower aspect 

 strictly as a problem in amphibian embryology with such general 

 references to wider questions as has been required to make clear 

 the history of the work in this field of research. 



JOURNAL OP MORPHOLOGY, VOL. 21, NO. 3. 



