AN ABSTRACT OF THE THESIS OF Roberta Jane Beeson for the degree of Doctor of Philosophy in General Science (Biological Science) presented on May 8, 1978 Title: BRIDGING THE GAP: THE PROBLEM OF VERTEBRATE ANCESTRY, 1859-1875 Abstract approved: Redacted for Privacy Paul Lawrence Farber Determination of the Vertebrate pedigree wasa particularly enigmatic problem for evolutionary morpholo- gists of the early post-Darwinian period. At that time, practically no characteristics were known by which the Vertebrates could be linked to any of the other animal groups. Up to the 1850's, most research in embryology and anatomy had reinforced the idea that wide differences existed in the basic structural and developmental patterns of Vertebrates and animals belonging to other branches of the animal kingdom. As a result, morphological practice was affected by a strong tradition against comparison of Vertebrates and Invertebrates. With the acceptance of the evolutionary viewpoint, it became theoretically valid to compare animals of different types, based on the possi- bility of their remote common ancestry. However, the practical matter of demonstrating that relationship with concrete evidence proved to be one of the most difficult challenges confronting early evolutionary morphology. Three different theories were proposed between 1864 and 1870, each attempting to link the Vertebratesand one of the Invertebrate groups to a hypotheticalcommon ancestor. In 1864, Franz Leydig proposed an evolutionary relationship between Arthropods and Vertebrates; in1866, Ernst Haeckel attempted to connect Vertebrates with Roundworms; and in 1868, on the basis ofnew research by Aleksandr Kovalevskii, Haeckel proposed another theory which linked Vertebrates with Tunicates. The proposals which formed the basis of the Tunicate theory becamethe center of a heated debate in the late 1860's and early 1870's. As a result of new research and criticism related to this debate, Haeckel made significant modifica- tions in a revised version of the Tunicate theory which was published in 1874. In this dissertation, the problem of Vertebrate ancestry is presented as a testing ground for the newly- emerging principles of evolutionary morphology. The content and reception of the first three theories of Vertebrate ancestry are examined and compared and the development of the Tunicate theory is traced from its original form as a provisional hypothesis to its later form as a definitive theory. Particular emphasis has been placed on describing and analyzing the scientific work on which support and criticism of the various theories of Vertebrate ancestry was based, and in deter- mining the working principles that various morphologists applied in approaching the problem of Vertebrate ancestry. Such an emphasis demonstrates that a wide variety of philosophical, methodological and empirical concerns existed within the world community of evolutionary morphologists during the early post-Darwinian period. By testing the applicability of their various viewpoints to the solution of the problem of Vertebrate ancestry, these morphologists made significant contributions to the conceptual progress of evolutionary morphology, particularly to the development of a new, genetic concept of homology. O Copyright 1978 Roberta Jane Beeson Bridging the Gap: The Problem of Vertebrate Ancestry, 1859-1875 by Roberta Jane Beeson A THESIS submitted to Oregon State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy Completed 8 May 1978 Commencement June 1978 APPROVED: Redacted for Privacy Assoiate Professor of History of Science in charge of major Redacted for Privacy Chairman of Department of General Science Redacted for Privacy Dean of Graduate School Date thesis is presented 8 May 1978 Typed by Leona Nicholson for Roberta Jane Beeson ACKNOWLEDGMENTS This dissertation is dedicated to the memory of my mother, Dorothy Roberta Robinson Beeson (1918-1976). She supported my ideas and work with interest, good humor, enthusiasm and financial help that far exceeded the limits of ordinary maternal concern. Hers was a rich and lively imagination and a generous and loving spirit, whose gifts and whose example I shall always remember with gratitude. From the beginning stages of research up to the final stages of preparing this dissertation,I have been helped and encouraged by many people whose contributions I am glad to acknowledge. Dr. Paul Farber has been an ideal advisor and major professor. I am very grateful for the flexibility and patience he has shown in accommodating to the problems of transcontinental and trans-Atlantic advising. His comments on my ideas and my writing have been insightful, concise and constructive, and he has shown great sensitivity in always including words of encouragement along with those of criticism. I am thankful to Leona Nicholson for attending to numerous administrative details connected with my in absentia status from Oregon State University. Her efficiency and thoughtfulness have allowed me to do my research and writing with a minimum of anxiety about regulations and deadlines. I am also grateful for her generosity in helping me with the technicalities of typing and manuscript preparation. Over the years that I have been using materials from the Library of the Museum of Comparative Zoology at Harvard University,I believe that practically everyone on the staff of that remarkable library has come to my rescue at one time or another. I am most grateful for the consistently cheerful attitude and efficient service of the various staff members who have patiently tracked down obscure journal articles for me, deciphered numerous foreign phrases and, titles, and renewed and re-renewed my long list of borrowed books and articles for as lbng as I have needed them. I especially thank Mina Brand for the many times she helped me with difficulties of German translation. It has been a privilege and a pleasure to entrust the illustration of this dissertation to Eliza McFadden. From my rough sketches and vague directions she has designed and produced a set of drawings that are attrac- tive as well as instructive. I am also grateful for her help with the difficult job of producing the figures that are copies of plates from nineteenth century treatises. I am thankful for many friends whose concern for my well-being and success in this venture has been a constant source of encouragement, especially Roger and Bertha Blaisdell, Bill and Martha Monbleau, Margaret Osler and Sarah Parker. Muriel Blaisdell has been the main sounding board for my ideas and observations during this project. I thank her for the hours she spent listening to my lengthy discourses on subjects that ranged from Tunicate embryo- logy and insect anatomy to the perplexities of the German language; for our many hours of creative and enjoyable dialogue on the history of biology; and especially for the moments of laughter we shared that help keep the problems and difficulties of research and writing in proper perspective. TABLE OF CONTENTS I. INTRODUCTION 1 Notes 16 II. EARLY SPECULATIONS ON VERTEBRATE ANCESTRY 17 The Arthropod Theory of Franz Leydig 19 The Sagitta Theory of Ernst Haeckel 63 Notes 84 III. AMPHIOXUS AND ASCIDIANS: AN UNSUSPECTED ALLIANCE 89 Notes 132 IV. THE TUNICATE THEORY OF VERTEBRATE ANCESTRY: 1868-1871 137 Ernst Haeckel's Proposal of the Tunicate Theory 138 Early Response to the Tunicate Theory 152 Theoretical and Empirical Contributions of Carl Gegenbaur 182 Gegenbaur and the Evolutionary Interpretation of Homology 201 Alternate Views on Homology: Lankester and Mivart 217 Charles Darwin and the Tunicate Theory 231 Further Studies on Ascidian Development 241 American Response to the Tunicate Theory 247 Notes 253 V. THE TUNICATE THEORY, 1872-1875: NEW DIRECTIONS 262 New Criticism and New Observations: Alfred Giard and Carl Kupffer 263 New Assumptions: The Gastrea Theory 285 New Support for the Theory: Eduard Oscar Schmidt 292 More New Investigations: Hertwig, Fol and Willer and the Endostyle 299 The Anti-Darwinian Opposition 308 The Old Embryology and the New Embryology 326 A New Version of the Tunicate Theory 335 The Annelid Theories of Carl Semper and Anton Dohrn 356 Notes 364 VI CONCLUSION 372 Notes 387 BIBLIOGRAPHY 388 LIST OF ILLUSTRATIONS Figure Page 1 Comparison of Arthropod and Vertebrate structure 23 2 Anatomy and histology of the insect brain 43 3 Histological structure of the insect nerve cord 44 4 Anatomy of Amphioxus and Sagitta 67 5 Early stages of development in Amphioxus 96 6 Later stages of development in Amphioxus 97 7 Anatomy of Simple Ascidians 107 8 Early stages of development in Simple Ascidians 109 9 Later stages of development in Simple Ascidians 110 10 The blood-relationship of Vertebrates and Invertebrates (ontogeny) 142 11 The blood-relationship of Vertebrates and Invertebrates (anatomy) 143 12 Ontogeny of Ascidians and Amphioxus 343 13 Anatomy of an Ascidian, Amphioxus, and larval lamprey 345 BRIDGING THE GAP: THE PROBLEM OF VERTEBRATE ANCESTRY, 1859-1875 I. INTRODUCTION When Charles Darwin (1809-1882) published the Origin of Species in 1859, the group of animals called the Vertebrata was a well-known and distinctive sub- division of the animal kingdom which included the five most familiar classes of animals--fish, amphibians, reptiles, birds and mammals. The members of these five classes were recognized as Vertebrates and distinguished from the rest of the animal kingdom by the possession of a number of exclusive features pertaining to their general body organization. In addition to the Vertebrata, zoologists recognized from three to six Invertebrate groups, each marked off from the others by its own particular constellation of, characteristics. Animals within each of these large branches were further classi- fied according to a hierarchical system of subdivision, including classes, orders, families, genera and species. Successively lower taxonomic levels in the system represented increasingly greater degrees of morphological similarity, or homology, among the animals within that rank.* *See Chapter 4 for a discussion of the use of the term homology in pre- and post-Darwinian morphology.