10 

 Growth and 

 Differentiation in 

 the Nervous System 



Rita Levi-Montalcini 



Department of Zoology 

 Washington University, St. Louis, Missouri 



In the course of divergence of cell lineages and Mocking out of differ- 

 ent systems from early products of division of the fertilized egg cell, 

 the nervous system is one of the first to assert its differentiation. The 

 thickening of the ectoderm along the middorsal line of the embryo 

 is a barely noticeable event among the many developmental processes 

 which take place at the same time. It is, however, a major event in the 

 history of the nervous system, which has dissociated itself from the 



* The work described in this paper was supported in part by grants from the 

 National Institute of Neurological Diseases and Blindness, Public Health Service, 

 Bethesda, Md., and from the National Science Foundation. Washington, D.C.. and 

 by a contribution from the American Cancer Society to Washington University, 

 St. Louis, Mo. 



The microphotographs were made by Cramer Lewis, Department of Illustration. 

 Washington University Medical School. St. Louis. Mo. 



261 



