6 THE BRAIN OF THE TIGER SALAMANDER 



choice, and the study of these animals has been so fruitful that by 

 far the larger part of my research has been devoted to them. 



In this work it was my good fortune to be associated with the late 

 G. E. Coghill, whose distinguished career pointed the way to an 

 original approach to the problems of the origins and growth of the 

 nervous organs and their functions. The record of phylogenetic his- 

 tory spans millions of years and is much defaced by time; but the 

 record of the embryonic development of the individual is measured 

 in days and hours, and every detail of it can be watched from mo- 

 ment to moment. The internal operations of the growing body are not 

 open to casual inspection, but Coghill showed us that the sequence 

 of these changes can be followed. 



He selected the salamanders for his studies for very good reasons, 

 the same reasons that led me to take these animals as my own point 

 of departure in a program of comparative neurology. My intimate 

 association with Coghill lasted as long as he lived, and the profound 

 influence which his work has had upon the course of biological and 

 psychological events in our generation has motivated the prepara- 

 tion of a book devoted to his career ('48). This influence, though 

 perhaps unrecognized at the time, was doubtless largely responsible 

 for my persistent efforts to analyze the texture of the amphibian 

 nervous system, for his studies of the growth of patterns of behavior 

 and their instrumentation in young stages of salamanders brought to 

 light some prmciples which evidently are applicable in phylogenetic 

 development also. 



While Coghill's studies on the development of salamanders were in 

 process, we were impressed by the importance of learning just how 

 these processes of growth eventuate in the adult body. This was my 

 job, and so we worked hand in hand, decade after decade, for forty 

 years. Progress was slow, but our two programs fitted together so 

 helpfully that my original plan for a comprehensive study of the 

 comparative anatomy of the nervous system was abandoned in favor 

 of more intensive study of salamanders. 



THE PLAN OF THIS BOOK 



The preceding details of personal biography are relevant here be- 

 cause they explain the motivation and plan of this book. The sig- 

 nificant facts now known about the internal structure of the brain of 

 the tiger salamander in late larval and adult stages are here as- 

 sembled. The observation's on this and allied species previously re- 



