Edwin G. Conklin

THE FORM AND ARRANGEMENT OF MICROTUBULES: AN HISTORICAL, PRIMARILY MORPHOLOGICAL, REVIEW

In the field of cell iology much ado is being made these days about filamentous cytoplasmic organelles. Microtubules, microfilaments, and 100 A filaments are invariably present in almost every cell that has been examined. Attempts to characterize these structures as to chemical composition, physical nature, and possible functions comprise a noteworthy proportion of the current efforts in the field of cell biology. In this symposium we will be brought up to date on the biology of microtubules, a field that has more than mushroomed in the last decade. Lest you grow too impressed with this decade of progress, I want to take the opportunity of this review to remind you that the existence of such structures as microtubules was predicted, as were some aspects of their behavior, long before microtubules were actually made visible by the electron microscope. Students of the structure of protoplasm, such as Flemming, Heilbrunn, Seifriz, Wilson, Frey-Wyssling, and Chambers, if sitting in this symposium today, would probably not be overly surprised by our “discoveries” about the existence and functions of cytoplasmic microtubules. The succession of theories describing the structure of protoplasm leads naturally to today’s ubiquitous microtubule. In this review we will move from an historical perspective through the development of our current picture of microtubule structures since the introduction of the electron microscope. After a cursory view of the various functions now attributed to microtubules, and of the arrangements of microtubules that have been associated with these functions, we will conclude with speculations about possible mechanisms by which ordered arrangements of microtubules may be generated.

Experimental studies on nuclear and cell division

During several seasons extensive experiments were made on the segmenting eggs of Crepidula plana. These experiments included a study of the influence on nuclear and cell division of hypertonic and hypotonic sea water, of ether, alcohol, etc., of the lack of oxygen, of the electric current, and of pressure and shaking. The following general conclusions may be drawn from this work: 1. Under the same treatment the effects may be extremely varied, owing, probably, to the different stages of cell division acted upon. 2. A dividing cell is much more easily disturbed or rendered abnormal than is a resting one; the mitotic figure in particular is very easily altered and most of the abnormalities observed arise from this source. 3. The earlier stages of cleavage are much more easily altered than are the later ones. 4. Certain general abnormalities occur after the most varied treatment, e. g., the general results both of concentration and of dilution of sea water are to produce polyasters and to prevent the cleavage of the yolk. 5. On the whole the results of the hypertonic solutions are the same whether they are produced by evaporation of the sea water or by the addition of NaCl, MgCl2, or KCl to sea water; in short, these salts exert no specific action on cell division. 6. The most general modification of the mitotic figure is the production of polyasters, multipolar spindles, and as a consequence, multiple nuclei. In many cases the cells are filled with asters and irregular mitotic figures, during division, while in the resting stage they are filled with equally numerous resting centrosomes and nuclei. 7. The movements of the chromosomes are in many cases interrupted, so that they remain scattered along the spindle, while the cytoplasmic movements are frequently stopped or altered.

CLEAVAGE AND DIFFERENTIATION IN MARINE EGGS

I I presume I have been invited to contribute to this monograph largely because I represent a link with the past-a kind of living fossil. It is now just sixty years since I began to study cleavage and differentiation in marine eggs, and, inasmuch as modern workers rarely refer to work that is more than twenty-five years old and never to that of the previous century, unless it be some notable monograph or compendium, it may be well that a voice from the past should recall some of the foundations on which modern cytology has been built. In these past sixty years, I have witnessed several changes of fashion in biological research and publication, some radical changes in cytological and embryological techniques, and some revolts against older methods and results, which were hailed by their leaders as the beginnings of new eras. The older fashion of work and publication was to spend years on some research and then to publish results in a mature and comprehensive article or monograph. The newer fashion ran to shorts, weekly or monthly reports, with frequent additions and alterations. In the 1890’s Jacques Loeb advised, “One idea, one paper.” But the ratio was not often as simple as that; frequently ideas were inversely proportional to the square of publications. The older fashion was to avoid repetition, the newer to expect to be heard for much speaking and writing, and to gain reputation and position by a multitudinous, even if miniscule, bibliography. Professor Farlow of Harvard University once compared such progress with that of the squid, which moves rapidly backward, at the same time emitting large quantities of ink. The so-called new eras in science have usually proved to be only stages in the continuous progress of knowledge. If one takes a long view of advancement in any field, it is evident that later work is always based on that which has gone before. A catastrophic theory of progress in science is as erroneous as a similar theory in geology and cosmogony. Such concepts are survivals of the old special creation idea according to which each species, each era, each advance is a new creation, unrelated to what has gone before. One of the most valuable results of the theory of evolution is the doctrine of the relatedness of all natural phenomena. Perhaps it is natural that younger generations should say, “Behold, we are the people and wisdom was born with us,” as it is also natural that the older and disillusioned should say or think, “Lo, we were the people and wisdom will die with us.” Both such opinions, however, are equally exaggerated. In biology, one of the principal revolts of the past half century has been against the old type of morphology, which dealt only with dead materials -a revolt against the study of life with the life left out. Formerly, morphology was largely that. Professors of morphology and journals of mor-

THE TWENTY-FIFTH ANNIVERSARY OF INITIATION OF RESEARCH IN THE CARNEGIE INSTITUTION OF WASHINGTON

THE founding of the Carnegie Institution of Washington was of peculiar significance as an influence turning attention toward advancement of knowledge, as contrasted with its restatement or transmission. The establishing of an agency for this specific purpose did not indicate that such activities were considered either more or less important than educational work. It presented rather a coordinate or supplementary program, which would naturally gear itself closely to that of institutions designed initially for the work of education, or for other special applications of knowledge. A group of the principal departments originated in 1904. Among them were Terrestrial Magnetism, Mount Wilson Observatory and Experimental Evolution. The last of these formed the basis for development of the present department of genetics. In the history of the institution many types of organization have been used, and there have been numerous changes in statement of program. So the contribution of Mrs. Harriman, through gift of the Eugenics Record Office with its generous endowment, led in 1921 to union of eugenics and experimental evolution in the Department of Genetics. In somewhat similar manner the Division of Plant Biology, established in 1928, shaped itself to embrace the work of six sections, including physiology of growth, photosynthesis or the utilization of solar energy by the plant, classification and its relation to heredity and environment, studies on the ifluence of aridity, the section concerned with relationships to environment, and one devoted to the history of plants. Development of the institution illustrates what have seemed to be the needs of organization in atteoptig to secure the largest measure of return in inveatigation. Recognition of research as in itself an essntial human activity had not attained the wide aceptance of the present decade, and much of the effort of the institution was given to support of investigation wherever opportunity might be found. The interest of Mr. Carnegie in discovery of genius or the exceptional man found expression in numerous spe-