This book deals primarily with the principal extracellular macromole-
cules of animal connective tissues. It attempts to answer some general
questions about the biological organization of the tissues: What is the
nature of this organization at various dimensional levels? What
functions does the organization serve? How has it evolved? I have given
major emphasis to the structures and properties of the macromolecular
components of extracellular matrices from a wide range of invertebrates
and vertebrates. In doing so, however, I have treated cursorily many
important aspects of connective tissue biology that appeared to be only
indirectly relevant to the principal questions asked. On the other hand,
I have not hesitated to search for broad biological principles outside
the prevailing conceptual boundaries of animal connective tissues and
the lower molecular dimensional levels. The numerous speculations
presented will, I hope, stimulate the reader to further thought and
investigation. Acknowledgements My previously unpublished data that have
been included in this volume could not have been obtained without the
generous gifts of specimens and other assistance by a number of
individuals and institutions. These are Dr. G. BERENSON of Louisiana
State University, Drs. W. P. BRAKER and D. ZUMWALD of the Shedd
Aquarium, Dr. S. H. CHUANG of the Univer- sity of Singapore, Dr. L. G.
CLARK and Mr. U. M. VARELA-DIAZ of the University of Pennsylvania, the
Government of Nicaragua, Dr. E. CLARK of Cape Haze Marine Laboratories,
Mr. C. E.