Book - Vertebrate Zoology (1928)

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Vertebrate Zoology G. R. De Beer (1928)

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Vertebrate Zoology

Vertebrate Zoology 1928.jpg

An Introduction To The Comparative Anatomy, Embryology, And Evolution Of Chordate Animals

By


G. R. de BEER, M.A., B.Sc, F.L.S.


Fellow Of Merton College, John Wilfred Jenkinson Memorial Lecturer In Comparative And Experimental Embryology In The University Of Oxford


With An Introduction By Julian S. Huxley, M.A.

Ullerian Professor Of Physiology Royal Institution


New York The Macmillan Company 1928


Printed In Great Britain By William Clowes And Sons, Limited, London And Beccles


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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)


To Kitten And Anne


Author's Preface

There are two methods of teaching Zoology. One method is to deal with a limited number of selected types one by one, and the other is to compare corresponding parts of a number of different animals. Each method has its advantages and its drawbacks. The type method is essential for gaining acquaintance with actual animals, and is of fundamental importance from the fact that it permits of practical study of the complete animals themselves. It cannot be too much emphasised that Zoology is the study of animals, and not the study of books written about them. That being so, it is obviously more convenient to dissect and study one type thoroughly before passing on to the next, than to have a number of dissections of corresponding portions of several animals all going on at the same time. The first two parts of this book are devoted to a study of types carefully selected so as to be of the greatest utility in the interpretation of other forms. Part I deals with the adult structure, and Part II with the modes of development.


While the type method is necessary for a start, it is attended with certain dangers. Too much attention may be paid to the types themselves and too little to the other animals of which they are but only in a general way typical. There is also the danger that "... a multitude of facts overcrowd the memory if they do not lead us to establish principles. ..." I have sought to remedy this with the help of a comparative treatment of the various organ-systems, which forms the subject of Part III. In this part, the information obtained in Parts I and II is woven into a framework, and other animals of interest are interpolated, so as to present a general view of the organ-systems from the evolutionary and functional points of view. By this means, it is possible to mention the significant points of certain animals which are unsuited to be taken as types in themselves. In many cases these interpolated animals are fossils, from the fragmentary knowledge of which it would be impossible to construct a sufficiently instructive type.


The use of this comparative treatment following upon the descriptions of types entails a certain amount of repetition, and this is intentional. Unfamiliar facts, which by themselves may be devoid of any particular interest, acquire an added attractiveness and significance when they are introduced under more than one setting.


Lastly, in Part IV the types and comparisons are woven together into a whole, and treated as a history of the chief groups of vertebrate animals. It is hoped that the general nature of the treatment of the characteristic features of vertebrates, and the inclusion of a section dealing with the affinities and evolution of the human race, may not be without interest for the human anatomist.


A few words may be added with regard to the types. They are selected and treated not only for their intrinsic importance, but also as introductions to the next types. The description of each type is therefore to some extent based on previous types. So the dogfish is not only an example of a primitive fish, but it also provides the material on which the disposition of the arterial arches and cranial nerves may be studied, and the knowledge so obtained is used in the interpretation of all higher types. Similarly, Gadus serves as an introduction to the bones of the skull, and Triton introduces the limb of the land- vertebrate. This must explain what may appear to be a lack of balance in the treatment of certain types.


Apart from the more ordinary dissections and observations which I have been able to make personally, I am indebted for sources of information chiefly to the teaching of the Oxford school of Zoology, and in particular to Professor E. S. Goodrich, F.R.S., whose principles I have largely attempted, however unsuccessfully, to follow. I wish to record my gratitude to him for his general guidance in many matters, and for the facilities which I have enjoyed in the Department of Zoology and Comparative Anatomy of the Oxford University Museum.


On occasion, I have had the privilege of discussing certain matters with Professor G. Elliot Smith, F.R.S., Professor C, Judson Herrick, Professor J. P. Hill, F.R.S., Professor Sir Charles Sherrington, O.M., F.R.S., Professor W. J. Sollas, F.R.S., Professor A. Thomson, and Professor D. M. S. Watson, F.R.S. To all of them I wish to make due acknowledgment for the help which their information and advice have afforded me. To my friend and colleague Mr. B. W. Tucker I am especially indebted for reading the MS., and for making several valuable and helpful suggestions. I take great pleasure in recording my thanks to Professor Julian Huxley, without whose suggestion, interest, and persistent encouragement this book would have remained unwritten. It goes without saying that these gentlemen are not responsible for the errors which this book contains.


I have thought it inadvisable to burden the text with references. Instead, a short list of works is appended at the end of most of the chapters. I may mention here certain easily accessible works of great general utility in the study of vertebrates :

  • Abel, O. Die Stamme der Wirbeltiere. Berlin and Leipzig. 1919.
  • Brachet, A. Traite d'Embryologie des Vertebres. Paris. 1921.
  • Graham Kerr, J. Text-Book of Embryology. Vol. II. London. 1919.
  • Hyman, L. H. A Laboratory Manual for Comparative Vertebrate Anatomy. Chicago. 1925.
  • Ihle, J. E. W., and others. Vergleichende Anatomie der Wirbeltiere. Berlin. 1927.
  • Jenkinson, J. W. Vertebrate Embryology. Oxford. 1913.
  • Kellicott, W. E. Chordate Development. New York.
  • Kingsley, J. S. Comparative Anatomy of Vertebrates. London, 1927.
  • Kingsley, J. S. The Vertebrate Skeleton. London. 1925.
  • Lull, R. S. Organic Evolution. New York. 1917.
  • von Zittel, K. A. Grundziige der Palaontologie. Vol. II. Berlin. 191 8.


With regard to the figures, I have preferred to illustrate a few points thoroughly, rather than attempt to provide a picture of all the structures that are worthy of attention. In any case, a picture is but a poor substitute for the structure itself. The majority of the figures were drawn specially for this book from dissections and laboratory preparations, and my intention has been to show that the student should have no difficulty in examining for himself the structures here figured (and many more besides which are not figured in this book), in any fairly- well equipped laboratory. I am indebted to my wife for preparing the figures for press, and to the following authors and publishers for permission to reproduce figures : to the Delegates of the Clarendon Press for figs. 73, 74, 75, 88, 89, 92, 94, 95, 96, 101, 102, 109, no, 114, 115, 116, from J. W. Jenkinson's Vertebrate Embryology, and for permission to copy figs. 87, 90, 91, 93, 97, 98, 108, 113, from the same work ; to Professor G. Elliot Smith and Mr. Humphrey Milford for figs. 180, 181, 183, from Essays on the Evolution of Man ; to Professor Boule for fig. 182 ; to the Editor of the Quarterly Journal of Microscopical Science for permission to copy fig. 118 ; to Professor W. K. Gregory and the American Museum of Natural History for permission to copy part of fig. 158 ; to Professor L. Bolk for permission to copy fig. 123 ; to Professor W. J. Sollas for permission to copy fig. 182 ; and to Mr. B. W. Tucker and Mr. J. Z. Young for the loan of drawings of dissections.


In conclusion, I wish to express to Messrs. Sidgwick and Jackson my appreciation of the care and skill which they have so kindly shown in the preparation of this book.


G. R. de B.

Oxford, February, 1928.

Editor's Introduction

It is the aim of this series to provide a number of text-books covering different fields of animal biology, in order to obviate as far as possible the pedagogically unfortunate habit of trying to introduce subjects of more recent development as appendages to a single morphological theme. We may deplore the way in which morphology arrogates to itself an unfair share of the time-table in many zoological laboratories in this country *, but the fact remains that morphology, well taught and well linked-up with other branches, is still educationally the best discipline in zoology, and, more surely than any other branch of the subject, throws open windows on to those long vistas that enlarge the mind and satisfy intellectual aspirations. But, even if its own fascination is brought out, it can be taught so as to leave it isolated among the later-developed branches of biology, like a foreign body encapsulated in living, growing tissues.


Mr. de Beer and I had many talks over this book. In the first place, we felt that the average zoology student to-day was being expected to absorb far too much detail in a given time, and that as a result, he was often overtaxed and prevented from seeing the wood for the trees. The teacher's aim should be to use no more fact-material^ than is needed to embody the architectural design which intellectual vision has planned ; but enough to build it firm, on lasting foundations.


Our second point was the need for linking up the various branches of biology. Morphology has such merits as a self-contained discipline that these efforts at liaison are not always made. I should like here to point out some of the ways in which an isolated morphology comes up against a blank wall, but through which she can advance to new view-points once she has reached out her hand to sister branches of biology.


Morphology's central conception, Homology, is being modified by Genetics. Identical but independent mutation of genes, as is now recorded from several different species of Drosophila, shows that the conception of a common ancestor is no longer fundamental to the idea of homology.


Here we obviously approach orthogenesis. On the other hand, other orthogenetic ideas derived directly from morphological study melt away in the light of developmental physiology. Such phenomena as the progressive phylogenetic horn-development of various mammals, sometimes occurring independently in parallel stocks, need not after all imply orthogenesis in its strict sense of steady, determinate change of the germ-plasm. A study of the mechanism of the relative growth of parts shows, as Mr. de Beer points out (Chap. XLIII), that natural selection for increased size will automatically bring out the horn-growth, as what Darwin called a correlated variation.


Recapitulation too must be viewed differently as the result of studies on growth and on genetics. As D'Arcy Thompson pointed out in his Growth and Form, differences in proportion between related animals must be due primarily to differences in the growth-rates of the parts concerned. Later work has shown that the characteristic proportion of a part generally depends on the part continuing to grow at a different rate from the rest of the body for a long period. This being so, many cases of recapitulation are due solely to this differential growth. Schultz has shown that the foetuses of primates still show the limb-proportions characteristic of their adults, but less strongly marked. This is recapitulation : but it is also a direct consequence of long-continued differential growth. The same principles can be applied to the recapitulation of shell-form shown in the ontogeny of many Nautiloids, Ammonites, etc., and to the fact that vestigial organs are often of greater relative size in young stages.


Such studies also bear on the systematic side of morphology ; for where the growth-rates of two parts are markedly different, the animal has no fixed form. This is frequent in Crustacea and Insects, and may even occur in mammals, as Hinton has shown for voles. This obviously demands a revision of certain taxonomic ideas on the value of precise measurements of proportion.


The fact, first emphasised by Goldschmidt, that Mendelian factors frequently act by altering the rates at which developmental processes occur and the times at which they begin and end, rather than effecting qualitative changes ab initio, also bears on the problem. The eye of Gammarus is first scarlet, then darkens (at different rates according to the genes present) to or towards black. This is no proof that the ancestral eye was red, but depends on the physiology of melanin-deposition. Bolk, as a result of morphological study, has shown how frequently characters of early stages become prolonged into later life in the course of evolution ; his analysis enlarges the old concept of neoteny, and shows how much more common it is than usually supposed. This, however, is what the developmental physiologist would expect. If the time of appearance and relative importance of an organ depends upon the rate of some process, we are just as likely to have that rate altered in one direction as in the other, and therefore just as likely to have an embryonic character spread on to later stages as an adult character pushed back into earlier stages. The latter is recapitulation, the former the reverse ; and both depend, not upon some mysterious evolutionary urge, but upon simple developmental laws.


Other cases of recapitulation also become more intelligible in terms of other aspects of Entwicklungsmechanik. Why, for instance, are notochord, gill-slits, and arterial arches of amniote vertebrates recapitulated, while their limbs never recapitulate fins, and their gill-slits never recapitulate gills ? The answer seems simple. The recapitulated ancestral organs are necessities, as formative stimuli, for the production of adult structures ; the non-recapitulated ones are not.


" Racial senescence," so-called, is another morphological-evolutionary concept which looks very different when morphology makes contact with physiology, but lack of space forbids a discussion of this point here.


Finally, there is the bearing on morphology of functional modification. Most biologists do not seem to realize the extent to which functional modification occurs in the normal vertebrate body. It appears to be true, not only that the size of every muscle in the body depends upon function, but the size, direction, and structure of every tendon and bone ; the detailed conformation of the blood-system depends largely, or perhaps wholly, on hydrodynamic considerations ; the size of every gland is regulated by its function ; and even the nervous system does not escape. It is only in earliest development that structure precedes function : later, structure is the resultant of function.


The recognition of these facts demands a new attitude towards the genetic and evolutionary bases of structural change. To take but one example, it is disturbing but true to find that the differences in form and minute architecture of the human heel-bone which distinguish it from that of apes are due to functional modification in each generation — to the fact that we put our weight on it in a different way owing to our walking upright. It is also disturbing to realize that in other groups, function does not play this important role in moulding structure. In all holometabolous insects, the size and form of all hard parts come into being once and for all, without previous function, since they have not existed in the larva, or been used in the pupa, and without the chance of being later modified by function, since there is no further moult. Thus definitive form — the morphologist's raw material — is arrived at by quite a different method in the two highest groups of animals.


I have, I hope, said enough to show that certain aspects of vertebrate morphology will bear restating ; and Mr. de Beer's pages are themselves the best evidence of his success in achieving that restatement without abandoning any of the essentials which give morphology such value as a discipline in its own right.


JULIAN S. HUXLEY.


Contents

PART I Morphological Types illustrating the Different Stages of Organisation and the Trend of Vertebrate Evolution

1. The Vertebrate Type as contrasted with the Invertebrate

2. Amphioxus, a primitive Chordate

3. Petromyzon, a Chordate with a skull, heart, and kidney

4. Scyllium, a Chordate with jaws, stomach, and fins

5. Gadus, a Chordate with bone

6. Ceratodus, a Chordate with a lung

7. Triton, a Chordate with 5-toed limbs

8. Lacerta, a Chordate living entirely on land

9. Columba, a Chordate with wings

10. Lepus, a warm-blooded, viviparous Chordate


PART II Embryological Types Illustrating the Modes of Development

11. The development of Amphioxus

12. The development of Rana (the Frog)

13. The development of Gallus (the Chick)

14. The development of Lepus (the Rabbit)

PART III Comparative Zoology of Chordates

Outline Classification of the main groups of Chordate animals showing the value and extent of comprehensive terms

15. The Blastopore

16. The Embryonic Membranes

17. The Skin and its derivatives

18. The Teeth

19. The Coelom and Mesoderm

20. The Skull

Table of Vertebrate Bone

21. The Vertebral Column, Ribs, and Sternum

22. Fins and Limbs

23. The Tail

24. The Vascular System

25. The Respiratory system

26. The Alimentary system

27. The Excretory and Reproductive systems

28. The Head and Neck

29. The functional divisions of the Nervous system

30. The Brain and comparative Behaviour

31. The Autonomic Nervous system

32. The Sense-organs

33. The Ductless glands

34. Regulatory mechanisms

35. Blood-relationships among the Chordates

PART IV Evolutionary Morphology

36. The bearing of Physical and Climatic factors on Chordates

37. The origin of Chordates, and their radiation as aquatic animals

38. The evolution of the Amphibia : the first land-Chordates

39. The evolution of the Reptiles

40. The evolution of the Birds

41. The evolution of the Mammalia

42. The evolution of the Primates and Man

43. Conclusions


Classification of the animals and groups of animals mentioned in this book



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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)
Vertebrate Zoology 1928: PART I 1. The Vertebrate Type as contrasted with the Invertebrate | 2. Amphioxus, a primitive Chordate | 3. Petromyzon, a Chordate with a skull, heart, and kidney | 4. Scyllium, a Chordate with jaws, stomach, and fins | 5. Gadus, a Chordate with bone | 6. Ceratodus, a Chordate with a lung | 7. Triton, a Chordate with 5-toed limbs | 8. Lacerta, a Chordate living entirely on land | 9. Columba, a Chordate with wings | 10. Lepus, a warm-blooded, viviparous Chordate PART II 11. The development of Amphioxus | 12. The development of Rana (the Frog) | 13. The development of Gallus (the Chick) | 14. The development of Lepus (the Rabbit) PART III 15. The Blastopore | 16. The Embryonic Membranes | 17. The Skin and its derivatives | 18. The Teeth | 19. The Coelom and Mesoderm | 20. The Skull | 21. The Vertebral Column, Ribs, and Sternum | 22. Fins and Limbs | 23. The Tail | 24. The Vascular System | 25. The Respiratory system | 26. The Alimentary system | 27. The Excretory and Reproductive systems | 28. The Head and Neck | 29. The functional divisions of the Nervous system | 30. The Brain and comparative Behaviour | 31. The Autonomic Nervous system | 32. The Sense-organs | 33. The Ductless glands | 34. Regulatory mechanisms | 35. Blood-relationships among the Chordates PART IV 36. The bearing of Physical and Climatic factors on Chordates | 37. The origin of Chordates, and their radiation as aquatic animals | 38. The evolution of the Amphibia : the first land-Chordates | 39. The evolution of the Reptiles | 40. The evolution of the Birds | 41. The evolution of the Mammalia | 42. The evolution of the Primates and Man | 43. Conclusions | Figures | Historic Embryology



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