References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Subject Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Author Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 . . . . . . . . . . . 6 Introduction Chondrification of the somitic mesoderm producing the primordia of the vertebrae has been a favourite topic of investigation by those interested in understanding the me- chanisms underlying development and differentiation. Study of this tissue involves the investigation of cell proliferation, migration and cytodifferentiation, synthesis of extra cellular matricial products, inductive tissue interactions, and tissue morphogenesi- some of the major unsolved problems of modern developmental biology. The topic is a large one and various aspects have been reviewed in the past, notably by Holtzer (1959; 1961), Lash (1963a), Strudel (1967), Lash (1968a, c), Holtzer (1968), Holtzer and Abbott (1968), Holtzer and Mayne (1973) and Levitt and Dorfman (1974). Feel- ing that the time was appropriate for a overview of the whole field of somitic chondro- genesis, I have prepared the present monograph. It covers the development of experi- mental studies from the initial grafting of somites to avian chorio-allantoic membranes in the 1920's, through the extirpation experiments of the 1940's, the culturing of the 1950's and the search for pure inducers, to the refocussing of attention on the environ- ment and matrix procucts which is dominating the studies of the 1970's. Many of the studies have utilized the embryonic chick as the experimental animal.