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Richards A Outline of Comparative Embryology. (1931)

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This historic 1931 embryology textbook by Richards was designed as an introduction to the topic. Currently only the text has been made available online, figures will be added at a later date. My thanks to the Internet Archive for making the original scanned book available.

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Pages where the terms "Historic" (textbooks, papers, people, recommendations) 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, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History \| Historic Embryology Papers)

Outline of Comparative Embryology

By

Aute Richards

Professor of Zoology

University of Oklahoma

New York John Wiley 8: Sons, Inc. London: Chapman & Hall, Limited 1931

1951

Preface

As the result of a number of years of experience in introducing students to the subject of embryology, the writer has found it desirable to ‘depart from the common practice of studying chiefly the special embryology of the chick, pig, and perhaps of amphioxus and the frog, and to devote much attention to the principles of general embryology. This procedure is based upon the assumption that a broad background of general knowledge forms a desirable starting point for the study of special embryology to be taken up later. As comparative anatomy has proven to be the best basis for the later study of anatomy, so comparative embryology forms a proper basis for a study of special embryology. Unfortunately there has been no book in our language which brings together in a small compass the principles of general comparative embryology.

In this book it is the aim to set up the general principles of development so that the student may see how his special case—chick, starfish, or other form—is merely one of several types and what its relation to the other types may be. The writer holds that the most effective presentation of the subject matter of embryology is the laboratory study of desirable types, supported by text-book and “quiz” work on these forms and accompanied by the consideration from a comparative standpoint of the broad principles of the subject, such as types of egg structure, of cleavage, of gastrulation, and the critical consideration of classical embryological doctrines, etc. To present the material in brief form for this general part of a course in Comparative Embryology this volume is designed. '

In Part One are taken up those phases of development which are passed through in the embryology of most higher forms of animals. A comparative study of these phases no doubt forms the basis of ninetenths of the courses in this subject. Of the vast amount of material from which choice must be made, the decision as to whether any certain topic should be discussed has been based always upon a single criterion. It is sought to show only how the single-celled fertilized egg arrives at the multicellular condition characteristic of the fully formed, but undifferentiated, young organism in which the organ systems are established. In an outline of comparative embryology it is not possible to follow through all the details nor to repeat descriptions whose general features apply to more than one kind of animal. Nor is it possible to follow through for these forms the later stages in their development and differentiation. If completeness were the goal, it would be necessary to include the special embryology of the many forms about which investigators would desire information, an obviously impossible task. It is hoped, however, that a basis is here laid for understanding the detailed embryology of any of the types and for working out later stages in whatever group the student’s interest may lie.

Part Two considers numerous miscellaneous problems that have arisen in connection with the history of embryology. Here the choice of topics has been governed largely by questions asked by students both beginning and more advanced. No attempt is made to cover all the classical topics of embryology, nor to arrange the ones chosen in an order to develop any particular thesis. It is simply thought to satisfy in some measure student interest in them and to make them easily available. Discussions of many of them are not available in brief form in any English text, although they concern matters about which students of zoology should be informed, for they are chiefly problems of normal development.

The embryology of the present day is experimental embryology. Its aim is to secure an insight into the real nature of those steps by which a single-celled egg becomes a completed adult. An understanding of development in its true sense is its goal. Many aids to experiment used only by chemists or physicists in years gone by are now every-day tools of the embryologists, for descriptive embryology alone is inadequate to give a complete understanding of development. Yet experimental embryology runs the danger of considering only processes and those out of relation to structures. It is in structures that functions are inherent, for one cannot understand the workings of a machine with which he is unfamiliar. Morphology in its descriptive phases is therefore basic to a proper attempt to work out functional relations. Our admiration for the attempts to secure an intelligent conception of the mystery which underlies the pageant of development must not allow us to disregard the importance of a foundation of knowledge of descriptive embryology. Perhaps the errors which may be avoided by the study of descriptive embryology in its comparative phases may serve to recompense the student for the time lost from experimental embryology.

Undoubtedly numerous errors are to be found in this volume. Much that is discussed has been the subject of life-long study by many investigators and has concerned material collected from all over the world. To understand all adequately so that each may be mentioned correctly and weighted properly in a brief outline, is a task hardly to be accomplished, and many inconsistencies of treatment must be apparent to the reader. It must be borne in mind, however, that not an extended treatise but an outline of principles is the intent of the book, and the intent places many limitations upon what can be undertaken.

Acknowledgments are due for assistance in almost every section. The material treated in a work of this kind is by no means new, and it would be impossible to present any one phase of it without finding parallel treatment in some source of information available to students of embryology of this day. There is no claim to originality in the book, not even in the treatment of many chapters. The book will have served its purpose, however, if it appears to have sufficient pedagogical background and if it presents in sufficiently compact form these principles, many of which I think are not briefly summarized elsewhere in the English language, and which are needed to give students a basis for work in special embryology,-either medicalor experimental.

Korschelt and Heider’s “Lehrbuch der vergleiehenden Entwicklungs— geschichte” is a great treasure house of embryological learning to which constant reference has been made. In many places (particularly in Chapters VII and VIII, Part One) even their arrangement has been so much the best that only minor departures from it are to be found here. In others an entirely different organization of the same material is here adopted. But the debt to Korschelt and Heider is a very great one. I appreciate very mucl_1-the gracious verbal permission to use their material freely which was given me by both Doctors Korschelt and Heider. .”_

Drawings to illustrate ,the text are from many sources and not many are new. The writer is not impressed with the desirability of replacing pictures made by investigators on specialforms with new ones when the former are well known and of proven value. The drawings in every case are accompanied by a legend giving the name of the investigators to whom indebtedness is due.

Permission has been granted by the following publishers to make use of the figures indicated either as modified, or in the case of numbers 1, 2, 3, 135, 136, 142, 153, 1-81 of the figures themselves. By Henry Holt & Co. permission has been given to use from Loey’s “Biology and Its Makers,” our figures 1, 2, and 3; to use from Kellicott’s “General Embryology” our figure 5; from Kellicott’s “Chordate Development” our figures 135, 136, 142, 144, and 181; and from Lillie’s “Embryology of the Chick” our figures 151, 152. By P. Blakiston’s Son & Co., Inc., permission has been given to use from Folsom’s “Entomology with Special Reference to Its Ecological Aspects,” 3rd edition, our figures 117, 161, and 162; and from Patten’s “Embryology of the Pig,” figure 7. The Oxford University Press has permitted the use from Jenkinson’s “Vertebrate Embryology” of our figures 81 and 173. The Princeton University Press has granted permission to use from Conklin’s “ Heredity and Environment” our figures 7 and 8. The U. S. Bureau of fisheries has given permission to use from Herrick’s “American Lobster” figures 113, and 1973.. And William Wood & Co. have permitted the modification of figures from Bailey and Miller’s “Textbook of Embryology” represented in figures 140 and 141. Macmillan & Co., Ltd., has sold us permission to make use of our figures 103, 109, 110 from McBride’s “Textbook of Embryology, Vol. I, Invertebrate Embryology,” and of our figures 167, 168, and 170 from Graham Kerr’s “Textbook of Embryology, Vol. II, Vertebrate Embryology.” The graciousness of the various publishing companies in thus facilitating our work is deeply appreciated.

Especial acknowledgment for help in many ways including aid with the materials used and the reading of parts of the text is due to 1ny wife, Mrs. Mildred Hoge Richards. My colleagues of the Department of Zoology of the University of Oklahoma, Doctor A. O. Weese and Doctor A. I. Ortenburger have assisted with advice and have read portions of the text. Professor J. F. Paxton of the Department of Greek has aided me with questions of terminology. And finally my assistants Mrs. Celeste Whaley Taft and Miss Kara J. Fullerton have given the most painstaking attention to a multitude of details. To all of these I am deeply grateful.

A. R.

Historic Disclaimer - information about historic embryology pages
Pages where the terms "Historic" (textbooks, papers, people, recommendations) 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, interpretations and recommendations may not reflect our current scientific understanding. (More? Embryology History \| Historic Embryology Papers)

Cite this page: Hill, M.A. (2026, November 3) Embryology Book - Outline of Comparative Embryology. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Book_-_Outline_of_Comparative_Embryology

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Book - Outline of Comparative Embryology: Difference between revisions

Latest revision as of 11:37, 29 March 2019

Outline of Comparative Embryology

Table of Contents

Preface

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 Aute Richards
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+Professor  of Zoology
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+University of Oklahoma
 New York
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 ==Table of Contents==
+{|
-Part One General Embryology
+! width=300px|Part One General Embryology
+! width=300px|Part Two Embryological Problems
+|-
+|
 * [[Book - Outline of Comparative Embryology 1-1|Chapter I Historical Development of Embryology]]
 * [[Book - Outline of Comparative Embryology 1-2|Chapter II The Germ-Cell Cycle]]
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 * [[Book - Outline of Comparative Embryology 1-10|Chapter X Formation of the Mammalian Embryo]]
 * [[Book - Outline of Comparative Embryology 1-11|Chapter XI Egg and Embryonic Membranes]]
+|
-Part Two Embryological Problems
 * [[Book - Outline of Comparative Embryology 2-1|Chapter I The Origin And Development Of Germ Cells]]
 * [[Book - Outline of Comparative Embryology 2-2|Chapter II Germ-Layer Theory]]
 * [[Book - Outline of Comparative Embryology 2-3|Chapter III The Recapitulation Theory]]
-* [[Book - Outline of Comparative Embryology 2-4|Chapter Iv Asexual Reproduction]]
+* [[Book - Outline of Comparative Embryology 2-4|Chapter IV Asexual Reproduction]]
 * [[Book - Outline of Comparative Embryology 2-5|Chapter V Parthenogenesis]]
 * [[Book - Outline of Comparative Embryology 2-6|Chapter VI Paedogenesis And Neoteny]]
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 * [[Book - Outline of Comparative Embryology 2-8|Chapter VIII The Determination Problem]]
 * [[Book - Outline of Comparative Embryology 2-9|Chapter IX Ecological Control Of Invertebrate Larval Types]]
+|}
 ==Preface==
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 A. R.
-==Part Two Embryological Problems==
+{{Historic Disclaimer}}
-==Chapter IX Ecological Control Of Invertebrate Larval Types==
-Throughout the animal kingdom many diverse environmental relations surround the eggs and young so that many responses might be
-catalogued. Environmental influences find expression in the places
-where the eggs are laid, in the amount and kind of food provided for the
-young during the early development, in the different devices for their
-protection, in specialized modifications for accomplishing locomotion
-and other vital activities, and in many cases in the production of forms
-of larvae ‘which are totally different from the adult organisms. These
-special types of larvae present a great range of variations from the
-modes of direct development with which the student of the embryology
-of vertebrates is familiar. These larval types involve a metamorphosis
-to the adult form which may be more or less complete and which in
-such cases brings the growing organism into an environment quite
-unlike that of its earlier development; metamorphosis is necessary in
-those forms in which the food and habits of the adult are unsuitable
-for developing young. If we assume the sea to have been the original
-home of most primitive stocks, an assumption which is more or less
-common and seems in line with the fact that very many types of animals
-develop in a moist atmosphere or liquid medium, we should expect the
-majority of unusual larvae to be found in the species living in salt water.
-The transition from salt water to fresh or to the terrestrial forms of life
-has presented many difficulties to the developing young and as a result
-those animals which live in fresh water or are terrestrial are more often
-characterized by direct development than are the salt-water forms.
-It may be regarded as an axiom of development that sessile adults
-have active young. This activity has two obvious results; first, the
-species secures its dispersal through the migration of the young, and
-econd, it extends the range. The migration is commonly passive but
-over a period of time serves to extend the range of the species as successfully as if the adults themselves were able to move. To insure dispersal,
-vast numbers of gametes must be produced, for the chance method of
-fertilization that usually accompanies such cases results in a failure of
-very many eggs and sperm to become further activated, and of those
-eggs which are fertilized only a few can come to maturity. The larval mortality is very high indeed, for these young are the food of many
-species as well as the victims of physical forces and of their own inability
-to find continuously satisfactory conditions for growth. The vast number
-of eggs produced may be realized by reference to the turbot which produces 9,000,000 in a single season, the cod with 5,000,000, and to the
-flounder with 1,000,000. In higher animals the reproductive energy
-is conserved by various means for caring for the young during early life,
-but in marine forms this is usually not the case. The second consequence
-of larval activity is to bring the growing forms into an entirely difierent
-range. This is illustrated in the case of the lobster, which is a bottom
-feeder, lurking in the crevices between stones and elsewhere to capture
-whatever prey may come within its reach, or feeding upon such dead
-forms as may be found nearby. The larvae, up to the time of the fourth
-molt, however, swim at the surface of the sea water. In addition to this,
-they are positively phototropic to light of the intensity of ordinary
-daylight, but the adults are negative. Thus the pelagic larvae are brought
-into a range of environment where their food, which consists of plankton,
-especially copepods, is abundant. Special structural modifications adapt
-these larvae to their surface pelagic life. They are the better enabled to
-swim on the surface of the water because of the possession of exopods,
-the outer branches of the walking legs characteristic of lower crustaceans
-but not present in the adults of the higher forms. These are retained to
-the fourth molt, when they are cast off, being no longer useful; the larva
-then goes to the bottom. Herrick makes note of several changes in
-structure and instincts which take place at the beginning of the fourth
-stage, which marks the most surprising leap in the whole history of development. Among these are the following: the primitive swimming
-branches of the thoracic appendages are lost; the cuticle becomes shell—
-like, containing more lime; the pigments are denser, the colors brilliant,
-and the color pattern variable; otocysts are present and orientation is
-perfect; rotation of the great forceps is complete; the animal, during
-at least a part of this stage, moves toward the light and swims steadily
-at the surface with the great claws directed forward and held close
-together; the preying instinct is more marked; the fighting instinct,
-the instinct of fear, “feigning,” and hiding are all developed by the
-close of the fourth stage or in the fifth, when the animal goes to the
-bottom to stay. In many other animals similar gain is accomplished
-by a specialized form of larval structure. The larva finds itself adapted
-to-securing food which is suitable for it, and structures which have
-only temporary employment are present and useful. It follows, however,
-that the gain to the larva would become a loss if the subsequent stages
-in the life cycle were not radically changed in such a way as to enable
-the organism to undertake a new mode of life. In other words, metamorphosis in such cases is a necessity for bringing about those adaptations which fit the organism to live in its permanent environment and
-there to undergo those further changes which look toward the production of new germ cells.
-It is not usual to find metamorphosis in animals which live in fresh
-water, although there are some outstanding cases in which larvae
-totally unlike the adult are developed in species inhabiting fresh water.
-It may, however, be taken as a general rule that development in freshwater forms with the exception of certain few highly specialized cases
-is direct. Fresh water presents a great lack of constancy in living conditions as compared with those of the sea. With but few exceptions the
-bodies of fresh water lack sufficient depth and area to maintain even a
-low degree of constancy. Fresh water becomes heated much more easily
-than the sea, it freezes comparatively quickly, its streams are subjected
-to periods of flood during which the water runs rapidly and scours out
-the beds or overflows, and when it recedes leaves innumerable forms of
-life stranded to perish. Every stream has narrows and depths where it
-runs rapidly and flats where its current is slow, an environment in
-which the fragile larvae would scarcely be able to maintain themselves,
-and there are but few animals which go through an independent larval
-history in fresh water. The lack of suitability of fresh water to larval
-development without doubt explains why so many groups of marine
-animals have not been able to gain a foothold in fresh water. A very few
-sponges, almost no coelenterates, occur in this environment, and many
-groups of marine fish and ascidians, cephalopods, king crabs, and some
-of the worm groups have not a single representative in fresh water.
-Animals that cannot produce eggs which develop into young like the
-adult are prevented from gaining ‘a. foothold by such a changeable
-medium as fresh water. In addition to the difficulties of fresh-water life
-already noted, a zone of brackish water between the fresh water and
-the sea is itself an almost impassable barrier to the entrance of marine
-forms.
-Terrestrial life presents to developing larvae even more dangers
-than fresh water. To this situation is due the fact that in land forms
-development is either direct and fairly simple or else specialized with
-complicated devices for caring for the young during their immature
-period. The latter condition is illustrated by many forms of insects in
-which metamorphosis is complete, often involving very complicated
-life histories. Some of the disadvantageous features of the terrestrial
-ECOLOGICAL CONTROL OF INVERTEBRATE LARVAL TYPES
-environment are the following: temperature undergoes a wide range
-of variation, often passing quickly between the extremes. This condition is quite unknown in the ocean and is much less in fresh water.
-The very changeableness as well as the extremes of heat and cold are
-hardships for the developing larvae. The weight of the body is no
-longer buoyed up by water and must be supported at every moment.
-This involves consumption of much energy as compared with the almost
-passive drifting of larvae in aquatic habitats, and renders movement
-much more difficult and restricted. Food no longer streams by as in
-the contrasting case, but must be actively sought, is often very much
-more restricted as to kind, and presents an increased toughness since
-in the composition of land forms the percentage of water is much less,
-and the food is necessarily more difficult to find. The glare of daylight
-and the consequent difficulty of avoiding enemies puts the terrestrial
-larvae to a disadvantage which forms living in the subdued shadows of
-the water do not share. finally the rapid evaporation to which terrestrial forms are subjected requires special devices for protecting the soft
-exterior of the organism. A heavy shell, mucous glands, and other
-similar devices show what a serious drain upon the organism requirements of this kind cause.
-These considerations account in a large measure for the lack of
-uniformity in the occurrence of larval types throughout the different
-groups of the animal kingdom. The particular forms of larvae within a
-group are of adaptive rather than taxonomic significance.
-The general subject of the care of young animals was briefly but
-instructively discussed by Gamble in “The Animal World” (Holt and
-Company). Some of the ideas mentioned on the three preceding pages
-are suggested by his discussion. Gamble sums up the responses of
-animals to different environmental conditions in which the young must
-be produced as follows:* “We find isolated examples of the retention of
-the young by diminution in the size of the family. Speaking generally,
-marine animals pour their eggs broadcast, and leave their minute larvae
-to complete their metamorphosis unaided and unsheltered, but in
-every group there are malthusian species which not only restrict their
-families in number, but enclose them by protective envelopes. The
-varied experience of larval life in this curtailed and direct development
-supplants metamorphosis. The eggs become larger and the young
-stronger at birth.
-“In fresh water the limitation and protection of the family is more
-generally the rule. Insects and Amphibia are the only large classes
-‘ Quoted by permission of Henry Holt & Co.
-which go through their larval life in fresh water. But the protection
-is usually of the simplest kind and is confined to the earlier stages of
-development.
-“On land the insects form the only class in which the majority still
-pursues a free larval history. Others develop directly, either growing
-up into full stature without guidance or protection, or carried and fed
-by their parents for some time both before and after hatching.”
+{{Richards1931 TOC}}
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