McGRAW-HILL PUBLICATIONS IN THE ZOOLOGICAL SCIENCES METHODS AND PRINCIPLES E. J. Boell, CONSULTING EDITOR OF Baitsell . HUMAN BIOLOGY SYSTEMATIC ZOOLOGY Breland· MANUAL OF CoMPARATlVE ANATOMY Chapman · ANIMAL EcoLOGY Clausen . ENTOMOPHAGOUS INSECTS Goldschmidt . PHYSIOLOGICAL GENETICS Hau pt . FUNDAMENTALS OF BIOLOGY Hyman. THE INVERTEBRATES: PROTOZOA THROUGH CTENOPHORA (Vol. I) THE lNVER1'EBRATES: PLATYHELMINTHES AND RHYNCHOCOELA (Vol. II) ERNST MAYR THE INVERTEBRATES: AcANTHOCEPHALA, AscHELMINTHEs, AND Curator of the Whitney-Rothschild Collections ENTOPROCTA (Vol. III) The American Museum of Natural History Johannsen and Butt . EMBRYOLOGY m· INSECTS AND M YRIAPOUS Leach . FmrnTIONAL ANATOMY OF THE MAMMAL E. GORTON LINSLEY MMMiietttccchhaeelllfll aa·n nGddE FNTlaEinyRtlA o·rL F ·UPLHNAYDBSAOIMORLAEONTGTOYAR LYS MofA NINl!SAELC TO JL" nG·1E~N ERAL Purn101.0GY A.sDsoecpiaatret mPeronUfte nosisfvo eErr nsotiotfy mE oonfltoo Cgmayo lilafonogdryn Piaaanr ad. ~Cithoaliorgmy an Pearse · ANIMAL EcoLOGY Quiring . FUNCTIONAL ANATmn OF THE v ERTEBRA'l'ES ROBERT L. USINGER Rogers · TEXTBOOK OF Co::v!PARATIVE PHYSIOI,OGY Rogers · LABORATORY Ou·rLINES IN COMPARATIVE PHYSIOLOGY Associate Professor of Entomology • SSShhhuuullllll, ·· LEHavERoRuLEeUD,T IaITOnYdN Ruthven · PRINCIPLES m· ANIMAL B101,0GY Alotenr nZaotoel oMgUiecnmailvb eeNrros, imtIyne ntoecfrl anCta1atilirioefno, arPnl aiCar iosm m1i9s4s8io n Shull, LaRue, and Ruthven ·LABORATORY DIRECTIONS IN PmNcrp1;i;;s OF ANIMAL BIOLOGY Snodgrass . PRINCIPI,ES OF lNSI•lCT MORPHOLOGY Storer · GENERAL ZooLOGY Storer . LABORATORY MANUAL FOR GENERAJ, ZOOLOGY we ichert ' ANATOMY OF THE CHORDATES Weichert ·ELEMENTS oF CHoRDATF; ANATOMY Welch · LIMNOLOGY Wieman· AN INTRODUCTION TO VERTEBRATE EMBRYOLOGY Wolcott · ANIMAL BIOLOGY Wolcott and Powell ·LABORATORY GumE IN ANIMAL B101.onY There are also the related series of JJfcGraw-Hill Publications in the Botanical Sciences, of which Edmund W. Sinnott is Consulting Ediwr, and in the A.gri cultural Sciences, of which R. A. Brink is Consulting Editor. \'v\ NEW YORK TORONTO LONDON McGRAW-HILL BOOK COMPANY, INC. 1953 3cp_!J,JL - am 43.0 PREFACE The authors have long felt the need for a treatise on the principles and methods of taxonomy. Such a work should be useful not only as an adjunct to teaching but also as a reference work for the practicing taxonomist and as a source of information to the general biologist. An analysis and full statement of the often disputed principles on which the taxonomic method is based are urgently needed. We share the view of O. W. Richards (1947) that "it is less the findings of taxonomy than its principles and methods which need to be taught" and understood. We believe that taxonomy is an important branch of biology which deals not METHODS AND PRINCIPLES OF SYSTEMATIC ZOOLOGY only with the identification and classification of natural populations but Co~yright, 1953, by the McGraw-Hill Book Company, Inc. Printed in the with objectives that go well beyond these fundamental activities. United States of America. All rights reserved. This book, or parts thereof The teaching of taxonomic theory and method has been a seriously may not be reproduced in any form without permission of the publishers'. neglected phase of biology. Most formal courses in systematics have Library of Congress Catalog Card Number: 52-10335 concentrated upon the end products of taxonomic research and have not provided the student with a means for critically evaluating these end II products or for tracing the steps by which, they were attained. An under standing of taxonomic theory and practice is essential not only to the beginning and the practicing taxonomist but to all those who draw upon the results of his studies. This is true to a greater or lesser extent for all biological sciences, but in particular for such fields as ecology, population genetics, comparative morphology, anthropology, comparative physio logy, and applied biology. Sound taxonomy is a prerequisite to intelli gent conclusions in all these fields. At the present time there is no book available that deals compre hensively with the principles and methods of taxonomy. Available works are merely commentaries on the International Rules, or they deal with selected phases of taxonomic theory with occasional reference to taxo- }' ,)' ~ nomic practice. 6HBAHOTE~ / The treatment in this book of certain phases of systematic zoology ioc111cxoro YnKJmn•; ,______., has necessarily been restricted because of limitations of space. Collect Hll.U. JlOMOIOIOla ,/ ing techniques, for example, are so diversely specialized in each group of ?/f9!3698 animals and so completely covered in separate works that they are not discussed in detail. A full discussion of the phyla and classes of animals is considered beyond the scope of this work, although a listing is presented (Table 2). Nomenclature, although strictly a means to an end, has occupied a THE MAPLE PRESS COMPANY, YORK, PA. disproportionate part of the time and energy of taxonomists. One reason v vi PREFACE J>Rb'FACR VH for this is that the subject is inherently complex and that revisions of the colleagues at The American Museum of Natural Hit:1tory and in the Bio Rules become necessary from time to time, since the practicability of the svstematists Discussion Group at the University of California and at Rules, like that of any other code of law, can be tested only by applica Stanford University have done much to shape our thinking along the tion. A more fundamental reason is that a basic philosophy or theory Jines expressed in this book. We also acknowledge the role of several underlies the Rules of Nomenclature. This theory has not only tended to generations of students at the University of California, who have unwit change in the course of years (as, for instance, with respect to the signifi tingly provided opportunity to test the clarity and effectiveness of por cance of types), but some of it could not be fully understood until the tions of the manuscript during its formative stages. Their response has principles of taxonomy themselves were more clearly understood (e.g., been most helpful. treatment of infraspecific names). We feel, therefore, that a presentation Formal acknowledgment of quoted material is made through literature of the Rules of Nomenclature would be incomplete which does not deal citations. Special thanks are due to several colleagues who generously with the history of the field, or which omits a discussion of the basic gave of their time to read portions of the manuscript. Their detailed principles. We have attempted to present both these aspects. On the suggestions and criticisms were carefully considered and were in most other hand, it is not the purpose of this book to enter into nomenclatural cases adopted. To these readers should go a large share of credit for eontroversies. Since at this writing there is no edition of the Inter accuracy of statements. On the other hand, the authors individually and national Rules of Zoological Nomenclature which is accurate or up to rollectively assume the responsibility for the errors which undoubtedly date, we hope that the simplified review of the Rules in Part 3 of our book will be discovered. The following persons read the chapters indicated: may prove to be especially useful. At the same time, the treatment is H. E. Blackwelder (1 to 17); E. Dougherty (10 to 16); Alden H. Miller open to the criticism that it is an unofficial version of a highly technical (l to 9); C. F. W. Muesebeck (1to17); C. W. Sabrosky (1to17); M.A. and, at the moment, controversial subject. It has been our aim to make Cazier (4, 5, 8, and 9); G. G. Simpson (7); L. M. Klauber (7); H. LPvenr nomenclature comprehensible to the practicing taxonomist, leaving it to (7), and R. F. Smith (7). nomenclaturists to analyze the voluminous proceedings of the Inter Finally, we wish to express our sincere thanks to the secretaries, who national Commission and to debate the various issues of the moment. meticulously typed the various drafts of the manuscript and helped in In attempting to bring together the more important elements of checking the bibliography and in various other tasks conneded with modern taxonomic theory and practice, we have, of necessity, selected the preparation of this "·ork. our materials primarily from the point of view of the student of living Ernst Mayr animals and have chosen illustrative examples with preference from our E. Gorton Linsley mvn work. The problems of the paleontologist, microbiologist, and Robert L. Usinger botanist have been taken into consideration as far as practicable, but the New York, N. Y. Berkeley, Calif. materials of these groups are often sufficiently different to require different .January, 1953 approaches to the solution of taxonomic problems. Nevertheless, there is much common ground of theory and method shared by the workers in I these diverse fields, and it is to be hoped that at some time in the not too ) distant future all biological taxonomy may be viewed· as a single cohesive field. If this book, by focusing attention on the problems of the systema tic zoologist, serves as a step in that direction, one of its goals will have been achieved. If it also assists in stimulating a more critical evaluation of taxonomic theory and methods and in a wider dissemination of knowl edge concerning them, the authors will feel that their labors have been justified. It is well-nigh impossible to acknowledge sources in a book of this kind, which has grown out of the accumulated contacts and experiences of the three authors throughout their lives. Suffice it to say that our early teachers in Germany and at the University of California and om CONTENTS Preface PART 1. TAXONOMIC CATEGORIES AND CONCEPTS 1. Taxonomy, its History and Functions 3 2. The Species and the Infraspecific Categories 23 3. Classification and the Higher Categories 40 PART 2. TAXONOMIC PROCEDURE 4. Collecting and Collections 63 5. Identification and Taxonomic Discrimination 72 6. Taxonomic Characters 105 7. Quantitative Methods of Analysis 125 8. Presentation of Findings 155 9. Preparation of Taxonomic Papers 178 PART 3. ZOOLOGICAL NOMENCLATURE 10. Historical and Philosophical Basis of Nomenclature 201 11. The Principle of Priority 212 12. The Type Method and Its Signifieance 236 13. Specific and Infraspecific Kam es 246 11. Generic Names 261 l L5. Family Name s 271 I 16. Names of Orders, Classes, and Phyla 276 , I 17. Ethics in Taxonomy 279 I Bibliography 285 Glossary 301 Index 317 '" PART l TAXONOMIC CATEGORIES AND CONCEPTS l I , I CHAPTER 1 TAXONOMY, ITS HISTORY AND FUNCTIONS Taxonomy, or systematics, is the science of classification of organisms. The term taxonomy is derived from the Greek ra~is, arrangement, and vbµo~, law, and was proposed by de Candolle (1813) for the theory of plant classification. Systematics stems from the Latinized Greek word ystema, as applied to the systems of classification developed by the early 8 naturalists, notably Linnaeus (Systema naturae, 1735). In modern usage both terms are used interchangeably in the fields of plant and animal classification.1 Taxonomy is built upon the basic fields of morphology, physiology, ecology, and genetics. Like other scientific disciplines it is a synthesis of many kinds of knowledge, theory, and method, applied in this case to the particular field of classification. Its potentialities and its limita tions are largely those of the basic fields whose raw materials it utilizes. The first step in the resolution of any kind of biological knowledge is the classification of phenomena in an orderly system. This means ulti mately the naming, description, and classification of all plants and animals. Something of the diversity of organic nature and the magni tude of this task may be indicated by the following figures. There are now known more than one-third of a million species of plants, sixty times as many as at the time of Linnaeus (Merrill, 1943). Every year about 4,750 new species of plants are described. Including synonyms and subspecies, more than 1 million names were proposed for phanerogams and cryptogams between 1753 and 1942. l The number of known species of animals is much greater than that of plants and has been estimated at about 1 million (Table 1). Including 1. subspecies, there are probably more than 2 million named forms of animals, and new ones are being described at the rate of about 10,000 per year. For the insects alone, Metcalf (1940) calculates that l}~ million names are already applied. Accepting an estimate of 3 million probable insect species (Silvestri, 1929), and assuming that each species has on the average five distinct developmental or morphological phases, 15 million descriptions will eventually be required to characterize the stages of all insect species! When we superimpose the necessity for arranging 3 million species in a framework of higher categories expre8s- 1 For different. usage see '.\iason (1950). 3 TAXONOMIC CATEGORIES AND CONCEPTS TAXONOMY, l1'S lllSTORY AND FUNCTIONS 5 ing inferred natural relationships, and analyzing the population structure Greater specialization has been the inevitable consequence of the tre of the species concerned, something of the magnitude of the task facing mendous growth of our knowledge of living things. just one group of taxonomists may be seen. The objectives of taxonomy can only be achieved by sustained cooper HISTORY OF SYSTEMATIC ZOOLOGY ative effort. Furthermore, the ability of the individual taxonomist to The history of taxonomy may be divided into a number of periods. contribute to this effort depends on the breadth of his training as •vell These in turn correspond loosely to the various levels of taxonomy (alpha as on his native talent. The complexities of modern systematics, its taxonomy, beta taxonomy, gamma taxonomy, see below). Definitions dependence on related fields, the refinement of modern techniques, and of these periods facilitate the understanding of the progress that has the magnitude of the literature have made it inevitable that the days of been made in the field. The complexity of taxonomy must be kept in mind when studying its history. Progress in the taxonomy of various TABLE 1. E8TIMATED 1\UMBER OF KNOWN SPECIES OF RECENT ANIMAJ,S (Mayr) animal groups (and in the study of animals from different regions) has Protozoa. . . . . . . . . . . . . . 30 , 000 Linguatula . . . . . . . . 70 been very uneven. Taxonomy is most advanced in the most popular .Mesozoa. . . . . . . . . . . . . . . . 50 Chelicerata. . . . 35, 000 groups (birds, butterflies, mammals, some genera of beetles), while in Porifera. . . . . . 4, 500 Crustacea. . . . . . . . 25, 000 others it may still be on an elementary level. It is most advanced in Coelenterata. . . . . \), 000 Other arthropods Ctcnophora . . . . 90 (e xcl. insects) ..... . 13,000 the North Temperate Zone and lagging behind in the tropics and other Platyhelminthe~. 6,000 Insecta ... . 850,000 distant places. Consequently the three historical periods here outlined Acanthocephala . 300 Mollusca .................. . 80,000 are not strictly consecutive but largely overlapping. Rotifera. . . . . . . . . . . 1 , 500 Pogonophora .............. . 1 First Period-the Study of Local Faunas. The history of taxonomy is Gastrotricha. . . . . . . . . . . . . . . . 175 Bryozoa .................. . 3,300 Kinorhyneha. . . . . . . . . . . . . . . . 100 Brachiopoda .............. . 250 almost as old as man himself. Natives of even the most primitive tribes Nematomorpha.............. 100 Echinodermata ............ . 4,000 may be excellent naturalists, with specific names for local trees, flowers, Nematoda ..................... 10,000 Phoronidca ................ . 4 mammals, birds, fishes, and the more conspicuous (or most edible) inver Priapulida. . . . . . . . . . . . . . . . . . . ,5 Chaetognatha ............. . 30 tebrates. A tribe of Papuans in the mountains of New Guinea was N emertina. . . . . . . . . . . 75 0 Hemichordata ............. . 80 found to have 137 specific names for 138 species of birds. Only one Entoprocta. . . . 60 Tunicat a. . . . . . . . . . ...... . 1,600 Annelida . . . . . . . . . . . . . 7 , 000 Fishes ............. . 20,000 ;.;pecies was confused with another. Often the nomenclature of such Echiuroida. . . . . . . . . . . . . . . . . . 60 Reptiles and amphibians .... . 6,000 tribes is clearly binominal, with a generic and a specific name (Bartlett, Sipunculoidea......... . . . . . . . . . 250 Birds......... . ......... . 8,590 1940). Tardigrada. . . . . . . . . . . . . . . . . . . 180 Mammals ................. . 3,200 Several early Greek scholars, notably Hippocrates (460--377 B.c.) and Onychophora. . . . 65 Total ......... . 1,120,310 Democritus (465-370 B.c.) included animals in their studies. However, One of the objects of this tahulation is to indicate the relative size of the various only fragments of the works of these earlier authors are in existence. groups of animals. Even the smallest phyla have therefore been included, because Apparently it was Aristotle (384-322 B.c.) who brought together the they are quite important from the points of view of phylogeny and comparative knowledge of his time and formulated it into the beginnings of a science. anatomy. The number of species of birds is based on an accurate count. All other figures are estimates, subject to two sources of error. Only 60, 50, or 40 per cent A.ristotle did not propose a formal classification of animals, but he pro (or even less) of the existing species have as yet been described in many animal vided the basis for such a classification in his statement that "animals groups. On the other hand, in the less-known groups of animals, many populations ma~ be characterized according to their way of living, their actions, their have been described as full species which appear to be merely subspecies of widespread habits, and their bodily parts." He referred to such major groups of polytypic species. The two sources of inaccuracy thus cancel each other to some animals as birds, fishes, whales, and insects, distinguishing among the last extent. both mandibulate and haustellate types and winged and wingless con the untrained taxonomist are limited. The amateur will always play a ditions, and utilizing certain terms for lesser groups, such as Coleoptera most important role in assembling much of the raw material with which a~1d Diptera, which persist today. Aside from these larger groupings, the taxonomist works, but he needs a broad background and special his categories, according to Nordenskiold (1928) were but two in num training if he is to make direct taxonomic contributions of the quality ber, the genos and the eidos, "the latter corresponding to the individual which will be required in the future. Even the trained taxonomist can animal form-horse, dog, lion-the former to all combinations of a higher no longer cover the entire field in any major group of plants or animals. degree." The Aristotelian philosophy-it can scarcely be called a sys- 6 TAXONOMIC CATEGORIES AND CONCEPTS TAXONOMY, ITS HISTORY AND PUNGl'IONS 7 tern-sufficed for the students of animals for nearly two thousand years. It is only in the works of the immediate predecess?rs o~ Linnaeus that much justification, he has been called the father of taxonomy. In the we find more than probing attempts at ammal classificat10n. . tenth edition of his great work Systema naturae (1758) (Fig. 1), the The botanists were far ahead of the zoologists during this period, srnce binominal system of nomenclature was for the first time consistently they were the first to break away from the Aristotelian tradition a~d applied to animals, and this work became the foundation of systematic describe and classify local plants. From Brunfels (1530) and B~uhm zoology. In addition to his new system of nomenclature, the work of (1623) there has been a continuous refinement of conce~t~ and techmq~es Linnaeus was characterized by clear-cut species diagnoses and by the (e.g., Tournefort and Plumier). The contemporary wntrngs of zoologists adoption of a hierarchy of higher categories: genus, order, class. The methods of Linnaeus were by no means wholly original, but his eminently practical system was quickly adopted, expanded, and elaborated because of his great personal prestige and the influence of his students. It domi nated taxonomy for the next century, and most of the essentials of the Linnaean method are still components of modern taxonomy. It is generally assumed that Linnaeus accepted the doctrine of fixity of species, species tot sunt, quot f ormae ab initio creatae sunt. Indeed, despite certain evidence to the contrary (Ramsbottom, 1938), systematic concepts of the Linnaean period were static concepts. Higher classifica tion was largely mechanical and showed what we now recognize to be natural relationships only in cases where fundamental characters hap pened to be selected. The thinking of this period was characterized by the concepts of classical typological taxonomy. The species was the nondimensional species of the local naturalist. The particular impor tance of this period for the history of taxonomy is that at that time biology consisted almost entirely of taxonomy, and nearly all the eminent biologists of that day were taxonomists. Linnaeus was not only the classical representative of this first period of taxonomy, his work also heralded the coming of the second period. Although Linnaeus in his earlier writings (e.g., Fauna suecica, 1746) exemplified the local naturalist, he became more and more cosmopolitan FIG. 1. Carolus Linnaeus (1707-1778) and title page from the foundation work in in his later publications, utilizing the discoveries of naturalists in faraway systematic zoology. countries. Still, his philosophy remained that of the student of local I faunas, except that the Systema naturae was the product of the joint I (e.g., Gesner, Aldrovandi, and Belon) were, on the whole, still domi~ated labors of many local naturalists. nboym Aenricsltaottuerleia na ncdo nocfe pptsr inacnidp lessh oowf edc laosnsl.iyfi crauti~oinm. entOsf oafl l a thceon seiasrtl~inetr waSs eaclorneadd Py ewriiodeds-ptrheea dA icnc ethptea necigeh otef eEnvtho lucetinotnu. ry E(vMoaluutpieorntuarisy, tBhuofufgohn,t authors, the one who had the greatest influence on Linnaeus was John Lamarck, and many others), but it owes its firm foundation to the second stRhimaey il sap(r1ei6tci2iee7ss- 1ian7n 0da5 n)w,i mwhaohl,os , t rhaercrorouigvgnehidz eeadvt a tlhau eam tdiooifnrfee roenfn acbtueo rtbahel t s'hi:i~egm~hlnea rnt t.hci~le asgs se~infniucdsa ta~1i~0sdn­ cmpleiemrnioat dxs itdnau rttrheiend g hm istohtodere ysm toliyfd tddalxueor inonfog m tthyhe,e t nhpierne pevetieorieuonsd t hpo ef creieoxndpt luoarrnyad.t i orenIat. c hwTeadhs iasc hmgaroraavnced than did those who had gone before him (Raven, 1942). terized by an intense interest in the faunas of faraway places, in mag The type of taxonomy that is based on the study of local faunas nificent world voyages and expeditions, and in the accumulation of vast wrehaocshee dc ointstr ipbeuatkio inns twheer eg sroe aitn fSluweendtiisahl onna tsuurbasleisqtu Lenint nsatuedues n(t1s 7t0h7a-t1,7 w7~i)th, gnruamphbiecr st roef astpmeceinmt eonfs gfreonmer aa lal nodv efra mthieli ews.o rldC, hwahrliecsh Dpearrmwiitnte (d1 8th0e9 -m18o8n2o) Was the naturalist on one of these expeditions (Voyage of the Beagle) I' TAXONOMY, ITS HISTORY AND PUNC1'/0NS TAXONOMIC CA1'EGORIES A.VD CONCEPTS 8 of the theory of evolution on taxonomy has consequently been a greater and worked up some of its results. He became the world's leadit~~ preoccupation with phylogeny. · l' t f the Ci'rripedia (barnacles) and wrote a monograph of this Ernst Haeckel (1866), more daring and speculative than Darwin, specia is o · f h' · · roup that was authoritative. It was largely on the ba~1s o i~ expen- introduced (Fig. 3) the method of representing phylogeny by means of ;nces as a traveling naturalist and taxonomist that Darwm conceived the trees or branching diagrams (see Chap. 8). Although his formalized theory of evolution. Combined with the reading of Malthus's Essay on diagrams resemble but little those that are in use today, the method itself Po ulation it also gave him an answer to the problem of the_ ca~se of ,ms useful and stimulating, and it provided the taxonomist with a graphic ev~lution the theory of natural selection. It is more than a comcidenc)e means for expressing supposed relationships. The search for facts to that another traveling field naturalist, Alfred R. Wallace (1823-1913 , improve the designs of phylogenetic trees dominated biology during the sPcond half of the nineteenth century and led to a boom in the fields of comparative systematics, comparative morphology, and comparative 0mbryology. In taxonomy, in particular, it spurred the search for "missing links" and "primitive ancestors." These efforts were not "asted but led to a far-reaching understanding of the animal forms and to the establishment of a natural system that is still considered essentially ntlid. This was an exciting period in the history of taxonomy. Not only were new species and genera discovered daily, but with reasonable frequency eYen new families or orders. The reward of such exciting discoveries attracted the keenest minds to the field of taxonomy. Alas, the wealth of nature is not inexhaustible, and the period of major new discoveries in the higher animals was over well before the end of the nineteenth century. Those who were anxious to describe new orders, families, and genera had difficulty discovering them. As an alternative choice they resorted to the splitting of the existing categories. Some splitting was justified and led to an elucidation of classification by doing away with heterogeneous, polyphyletic groups. In other cases, however, it led to a disintegration of natural categories. It appears, in retrospect, as the most retrogressive period in the history of taxonomy. Few of the splitters were good biolo gists, nor did they understand the proper function of the taxonomic .· (1809-1882) and title page from the foundation work FIG. 2. Char1 e s Rob er t D am m ' categories. Part of the disrepute into which taxonomy fell during the in evolutionary theory. latter part of the nineteenth and early twentieth century was caused by \ came simultaneously to the same conclusions. T~e v~ews of both me~ the activities of those who unnecessarily split well-known and well l were jointly presented in 1858 to the Linnaean Society m ~n~ of the most founded taxonomic categories, thereby hopelessly concealing natural dramatic episodes in the history of science. That Darwm1sm was toha affinities. large extent based on taxonomic work is perhaps one of the. reasons w y Third Period-the Study of Populations. While the preceding period it did not actually alter taxonomic arrangements very basically, as has was dominated by the study of evolution of the higher categories, with a great interest in ancestral forms or missing links (such as Amphioxus or been pointed out by Dobzhansky (1951). . . The publication of Darwin's On the Orig~n of. Species (1859) (Fig. 2) Peripatus), the most recent phase in the history of taxonomy is charac resulted in a tremendous stimulation of b10logic~l ~bought and work. terized by a study of the evolution within species. The typological con The decades immediately following 1859 were prmc1pally taken up ~ cept of the species, which was already shaky in the preceding period, was 'i the question, Is evolution a fact? Or, stated different!!, Are tl~ t~: abandoned and replaced by a dynamic, polytypic concept. Interest livin or anisms descendants of common ancestors? The mteres o reverted to the fauna of local areas and to the study of variation within perio~ w!s preeminently phylogenetic. The chief effect of the acceptance JO '.l'AXONOMIC CATEGORIES AND CONCEPTS TAXONOMY, ITS HISTORY AND FUNCTIONS 11 p a c populations and the slight differences between adjacent populations. The taxonomist is no longer satisfied to possess types and duplicates; .he collects series and analyzes them quantitatively. This type of study was commenced almost simultaneously by ornithologists, entomologists, and malacologists in the second half of the nineteenth century. The detailed history of this phase of taxonomy has not yet been written, but it would be well worth the attention of historians of biology. Although the study of populations reached its dominant position in sys tematics only within recent generations, its roots go back to the pre Darwinian period. In ornithology, after the pioneer efforts of Schlegel, the systematic collecting of series was particularly in vogue among the American school, following the leadership of Baird (1854): As the object of the [Smithsonian] Institution in making its collections is not merely to possess the different species, but also to determine their geographical distribution, it becomes important to have as full series as practicable from each locality. . . . The number of specimens to be secured will, of course, depend upon their size, and the variety of form or condition caused by the different features of age, sex, or season. In gathering specimens of any kind, it is impor tant to fix with the utmost precision the localities where found. Among the malacologists are to be mentioned particularly Kobelt (1881), Gulick (1905), the Sarasins (1899), as well as Crampton, whose biometrical studies in the local geographical variation in the genus Partula (1916, 1932) have become classical. The results of this work caused the abandonment of the typological species concept. Species were no longer considered as something fixed m and uniform, but rather as polytypic, consisting of many subspecies and local populations, each differing from the others and each showing con siderable variability within itself. Two facts, in particular, were out standing. First, that the differences between subspecies and species were compounded of very numerous small variations; and second, that much of the local and geographical variation was closely correlated with the environment. The working and thinking of the leading taxonomists of this period was thoroughly modern and biologically correct, except in one respect. Most of them interpreted the close correlation between I, Frl1l: variation and the environment as indicating a direct effect of the environ Moue1·es jS tamMmboanuomph dyer lOetrigsacnhiesmr en t~ieanllty. muTchhe ycl owseerre t Loa tmhea rtcrkuitahn st.h anIn th sep ietaer olyf tMhiesn dererloiarn tsh. ey were essen iFnIsG a . f3o.r mTahle t rpehey-lloikgee ndyia ogfrlaimvi.bn g things as conce~;itvUe(Od~~ obnuy.D ~lHd~ a }e~,c'tmkllfeUsTlt~J /lf(e!1Jat 8ew~c6ttk6(eq)el .z~a eJinedundtae~ ,le v1xtJ8lpt6. . 6r...e .s..s. etd lf(ai.ien rlIg dte1 o9wmf0 a0ugs)te ,and taeuitonriinc nessg.v (etD.nh Hetis o wV wprheeiiervciseho ra d,en tvtdhhe eBan tteau attaerhlslelyoy nM M)l eeeadnnn dddteoe ltl iihtaahonneu s rg suehpmltee spct hhtwaaacestu irtzelhae errde y rdt ihpisseerco orodovful eectr eheodedf new species by a single step. They minimized the role of the environ-