CONTENTS Introduction.......................................................... The Adult Cell......................................................... The Embryo Cell........................................................ Comparison Between the Embryo and the Adult Cell....................... Conclusion.......................................................... INTRODUCTION In a preceding paper 1 one of us has shown with Lhermitte that the longest diameter of the motor cells of the anterior horn of the adult human spinal cord is in the cephalocaudal axis of the spinal cord and that this diameter is twice or more than twice the length of the dorsoventral and dextrosinistral diameters. At first sight this fact seems only of morphologic significance, only of importance in changing in textbooks of the anatomy of the nervous system the idea of the form of these cells by pictures of their three dimensions. If, however, we inquire more deeply into the details of this problem, we recognize that these new facts may furnish some new ideas about the relations between cellular form and function, and that something may be added