THE N. W. HARRIS LECTURES FOR 1914 were founded in 1906 through the generosity of Mr. Norman Wait Harris of Chicago, and are to be given annually. The purpose of the lecture foundation is, as expressed by the donor, "to stimulate scientific research of the highest type and to bring the results of such research before the students and friends of Northwestern Uni- versity, and through them to the world. By the term 'scientific research' is meant scholarly in- vestigation into any department of human thought or effort without limitation to research in the so- called natural sciences, but with a desire that such investigation should be extended to cover the whole field of human knowledge." 1907 Personalism. Borden P. Bowne 1908 University Administration. Charles W. Eliot 1910 The Age of Mammals. Henry F. Osborn 1911 Democracy and Poetry. Francis B. Gummere 1912 The Milk Question. Milton J. Rosenau 1913 The Constitution of Matter. Joseph S. Ames NORMAN W. HARRIS LECTURES FOR 1914 AT NORTHWESTERN UNIVERSITY HEREDITY AND ENVIRONMENT IN THE DEVELOPMENT OF MEN BY EDWIN GRANT CONKLIN PROFESSOR OF BIOLOGY IN PRINCETON UNIVERSITY PRINCETON UNIVERSITY PRESS PRINCETON LONDON : HUMPHREY MILFORD OXFORD UNIVERSITY PRESS 1915 Copyright, 1915, by PRINCETON UNIVERSITY PRESS Published February, 1915 PREFACE The origin of species was probably the great- est biological problem of the past century ; the origin of individuals is the greatest biological subject of the present one. The many incon- clusive attempts to determine just how species arose led naturally to a renewed study of the processes by which individuals come into existence, for it seems probable that the prin- ciples and causes of the development of indi- viduals will be found to apply also to the evolution of races. As the doctrine of evolu- tion wrought great change in prevalent be- liefs regarding the origin and past history of man, so present studies of development are changing opinions as to the personality of man and the possibilities of improving the race. The doctrine of evolution was largely of theo- retical significance, the phenomena of develop- ment are of the greatest practical importance ; indeed there is probably no other subject of PREFACE such vast importance to mankind as the knowl- edge of and the control over heredity and development. Within recent years the experi- mental study of heredity and development has led to a new epoch in our knowledge of these subjects, and it does not seem unreasonable to suppose that in time it will produce a better breed of men. The lectures which compose this volume were given at Northwestern University in February, 1914, on the Norman W. Harris Foundation and were afterward repeated at Princeton Uni- versity. I gladly take this opportunity of ex- pressing to the faculties, students and friends of both institutions my deep appreciation of their interest and courtesy. In attempting to present to a general audience the results of re- cent studies on heredity and development, with special reference to their application to man, the author has had to choose between simplicity and sufficiency of statement, between apparent dogmatism and scientific caution, between a popular and a scientific presentation. These are hard alternatives, but the first duty of a lecturer is to address his audience and to make PREFACE his subject plain and interesting, if he can, rather than to talk to the scientific gallery over the heads of the audience. In preparing the lectures for publication it has not been possible to avoid the technical treatment of certain sub- jects, but in the main the lectures are still addressed to the audience rather than to the scientific gallery. Unfortunately biology is still a strange subject to many intelligent people and its terminology is rather terrifying to the uninitiated ; but it is hoped that the glos- sary at the end of the volume may rob these unfamiliar terms of many of their terrors. I take this opportunity of thanking Dr. W. E. Castle and Dr. J. H. McGregor for the use of photographs which are reproduced in Figures 81, 82 and 99; and I wish especially to thank my assistant, Marguerite Ruddiman, for her aid in preparing figures and manu- script for publication. Princeton, December, 1914 vii CONTENTS CHAPTER I. FACTS AND FACTORS OF DEVEL- OPMENT INTRODUCTION A. PHENOMENA OF DEVELOPMENT I. DEVELOPMENT OF THE BODY 1. The Germ Cells 2. Fertilization 3. Cleavage 4. Embryogeny 5. Organogeny 6. Oviparity and Viviparity 7. Development of Functions II. DEVELOPMENT OF THE MIND 1 . Sensitivity 2. Tropisms, Reflexes, Instincts 3. Memory 4. Intellect, Reason 5. Will 6. Consciousness B. FACTORS OF DEVELOPMENT 1. Preformation 2. Epigenesis 3. Preformation and Epigenesis 4. Heredity and Environment ix CONTENTS Other Mendelian Ratios 2. Results of Crossing Individuals with more than one pair of contrasting characters Dihybrids and Trihybrids 3. Inheritance Formulae 4. Presence and Absence Hypothesis 5. Summary of Mendelian Principles a. The Principle of Unit Characters b. The Principle of Dominance c. The Principle of Segregation II. MODIFICATIONS AND EXTENSIONS OF MEN- DEHAN PRINCIPLES 1. The Principle of Unit Characters and Inheritance Factors Inheritance Factors and Germinal Units 2. Modifications of the Principle of Domi- nance Sex and Sex Limited Inheritance Sex Linked Inheritance 3. The Principle of Segregation "Blending" Inheritance III. Mendelian Inheritance in Man CHAPTER IV. INFLUENCE OF ENVIRONMENT A. RELATIVE IMPORTANCE OF HEREDITY AND ENVIRONMENT 1. Former Emphasis on Environment 2. Present Emphasis on Heredity 3. Both Indispensable to Development xii CONTENTS B. EXPERIMENTAL MODIFICATIONS OF DEVELOPMENT I. DEVELOPMENTAL STIMULI 1. Physical Stimuli 2. Chemical Stimuli II. DEVELOPMENTAL RESPONSES Dependent upon (a) Nature of Organism, (b) Nature of Stimulus, (c) Stage of De- velopment 1. Modifications of Germ Cells before Fertilization 2. During Fertilization 3. After Fertilization C. FUNCTIONAL ACTIVITY AS A FACTOR OF DEVELOPMENT D. INHERITANCE OR NON-INHERITANCE OF ACQUIRED CHARACTERS E. APPLICATIONS TO HUMAN DEVELOP- MENT: EUTHENICS CHAPTER V. CONTROL OF HEREDITY: EU- GENICS A. DOMESTICATED ANIMALS AND CULTI- VATED PLANTS I. INFLUENCE OF ENVIRONMENT IN PRODUCING NKW RACES II. ARTIFICIAL SELECTION 1. The Methods of Breeders 2. How has Selection acted? III. METHODS OF MODERN GENETICS 1. Mendelian Association and Dissocia- tion of Characters 2. Origin of Mutations xiii CONTENTS B. CONTROL OF HUMAN HEREDITY I. PAST EVOLUTION OF MAN II. CAN HUMAN EVOLUTION BE CONTROLLED? 1. Selective Breeding the only Method of Improving the Race. 2. No Improvement in Human Heredity within Historic Times 3. Why the Race has not Improved III. EUGENICS 1. Possible and Impossible Ideals 2. Negative Eugenical Measures 3. Positive Eugenical Measures 4. Contributory Eugenical Measures 5. The Declining Birthrate CHAPTER VI. GENETICS AND ETHICS I. THE VOLUNTARISTIC CONCEPTION OF NA- TURE AND OF HUMAN RESPONSIBILITY II. THE MECHANISTIC CONCEPTION OF NATURE AND OF PERSONALITY 1. The Determinism of Heredity 2. The Determinism of Environment III. DETERMINISM AND RESPONSIBILITY 1. Determinism not Fatalism 2. Control of Phenomena and of Self 3. Birth and Growth of Freedom 4. Responsibility and Will 5. Our Unused Talents IV. THE INDIVIDUAL AND THE RACE 1. The Conflict between the Freedom of the Individual and the Good of Society 2. Perpetuation and Improvement of the Race the Highest Ethical Obligation REFERENCES, GLOSSARY, INDEX xiv CHAPTER I FACTS AND FACTORS OF DEVELOPMENT CHAPTER I FACTS AND FACTORS OF DEVELOPMENT INTRODUCTION One of the greatest results of the doctrine of organic evolution has been the determination of man's place in nature. For many centuries it has been known that in bodily structure man is an animal; that he is born, nourished and de- veloped, that he matures, reproduces and dies just as does the humblest animal or plant. For centuries it has been known that man belongs to that group of animals which have backbones, the vertebrates; to that class which have hair and suckle their young, the mammals, and to that order which have grasping hands, flat nails, and thoracic mammae, the primates, a group which includes also the monkeys and apes. But as long as it was supposed that every species was distinct in its origin from every other one, and that each arose by a 3 4 HEREDITY AND ENVIRONMENT special divine fiat, it was possible to maintain that man was absolutely distinct from the rest of the animal world and that he had no kinship to the beasts, though undoubtedly he was made in their bodily image. But with the establish- ment of the doctrine of organic evolution this resemblance between man and the lower ani- mals has come to have a new significance. The almost universal acceptance of this doctrine by scientific men, the many undoubted resem- blances between man and the lower animals, and the discovery of the remains of lower types of man, real "missing links," have inevitably led to the conclusion that man also is. a product of evolution, that he is a part of the great world of living things and not a being who stands apart in solitary grandeur in some isolated sphere. But wholly aside from the doctrine of evolu- tion, the fact that essential and fundamental resemblances exist among all kinds of organ- isms can not fail to impress thoughtful men. Life processes are everywhere the same in principle, though varying greatly in detail. All the general laws of life which apply to animals and plants apply also to man. This FACTS AND FACTORS OF DEVELOPMENT 5 is no mere logical inference from the doc- trine of evolution, but a fact which has been established by countless observations and ex- periments. The essential oneness of all life gives a direct human interest to all living things. If "the proper study of mankind is man," the proper study of man is the lower organisms in which life processes are reduced to their simplest terms, and where alone they may be subjected to conditions of rigid ex- perimentation. Upon this fundamental like- ness in the life processes of man and other animals are based the wonderful advances in experimental medicine, which may be counted among the greatest of all the achievements of science. The experimental study of heredity, develop- ment and evolution in forms of life below man must certainly increase our knowledge of and our control over these processes in the human race. If human heredity, development and evolution may be controlled to even a slight extent, we may expect that sooner or later the human race will be changed for the better. At least no other scheme of social betterment and 6 HEREDITY AND ENVIRONMENT race improvement can compare for thorough- ness, permanence of effect, and certainty of results, with that which attempts to change the natures of men and to establish in the blood the qualities which are desired. We hear much nowadays about man's control over na- ture, though in no single instance has man ever changed any law or principle of nature. What man can do is to put himself into such relations to natural phenomena that he may profit by them, and all that can be done to- ward the improvement of the human race is to apply consciously to man those great princi- ples of development and evolution which have been operating unknown to man through all the ages. A. PHENOMENA OF DEVELOPMENT One of the greatest and most far-reaching themes which have ever occupied the minds of men is the problem of development. Whether it be the development of an animal from an egg, of a race or species from a pre-existing one, or of the body, mind and institutions of man, this problem is everywhere much the FACTS AND FACTORS OF DEVELOPMENT 7 same in fundamental principles, and knowl- edge gained in one of these fields must be of value in each of the others. Ontogeny and phylogeny are not wholly distinct phenomena, but are only two aspects of the one general process of organic development. The evolu- tion of races and of species is sufficiently rare and unfamiliar to attract much attention and serious thought; while the development of an individual is a phenomenon of such universal occurrence that it is taken as a matter of course by most people, something so evident that it seems to require no explanation; but famili- arity with the fact of development does not remove the mystery which lies back of it, though it may make plain many of the proc- esses concerned. The development of a human being, of a personality, from a germ cell is the climax of all wonders, greater even than that involved in the evolution of a species or in the making of a world. The fact of development is everywhere ap- parent ; its principal steps or stages are known for thousands of animals and plants ; even the precise manner of development and its factors 8 HEREDITY AND ENVIRONMENT or causes are being successfully explored. Let us briefly review some of the principal events in the development of animals, and particu- larly of man, and then consider some of the chief factors and processes of development. Most of our knowledge in this field is based upon a study of the development of animals below man, but enough is now known of hu- man development to show that in all essential respects it resembles that of other animals, and that the problems of heredity and differ- entiation are fundamentally the same in man as in other animals. I. DEVELOPMENT OF THE BODY The entire individual structure and func- tions, body and mind develops as a single in- divisible unity, but for the sake of clarity it is desirable to deal with one aspect of the indi- vidual at a time. For this reason we shall consider first the development of the body, and then the development of the mind. 1. The Germ Cells. In practically all ani- mals and plants individual development begins with the fertilization of a female sex cell, or FACTS AND FACTORS OF DEVELOPMENT 9 egg, by a male sex cell, or spermatozoon. The epigram of Harvey, "Omne vivum ex ovo>' has found abundant confirmation in all later studies. Both egg and spermatozoon are alive and manifest all the general properties of liv- ing things. How little this fact is appreciated by the public is shown by the repeated an- nouncements by the newspapers that "Profes- sor So-and-so has created life because he has made an egg develop without fertilization." An egg or a spermatozoon is as much alive as is any other cell; as characteristically alive as is the adult animal into which it develops. It is difficult to define life, as it is also to de- fine matter, energy, electricity, or any other fundamental phenomenon, but it is possible to describe in general terms what living things are and what they do. Every living thing whatever, from the smallest and simplest micro-organism to the largest and most com- plex animal, from the microscopic egg or spermatozoon to the adult man, manifests the following distinctive properties: (a) It contains protoplasm, "the material basis of life," which is composed of the most 10 HEREDITY AND ENVIRONMENT complex substances known to chemistry. Protoplasm is not a homogeneous substance, but it always exists in the form of cells, which are minute masses of protoplasm composed of many distinct parts, the most important of these being the nucleus and the cytoplasm ( Fig. 1 ) . Protoplasm is therefore organized, that is, composed of many parts all of which are integrated into a single system, the cell. Higher animals and plants are composed of multitudes of cells, differing more or less from one another, which are bound together and integrated into a single organism. Living cells and organisms are not static structures which are fixed and stable in character, but they are systems which are undergoing continual change. They are like the river, or the whirl- pool, or the flame, which are never at two con- secutive moments composed of the same particles but which nevertheless maintain a constant general appearance ; in short they are complex systems in dynamic equilibrium. The principal physiological processes by which all living things maintain this equilib- rium are: FACTS AND FACTORS OF DEVELOPMENT 11 N. Memb r FIG. 1. A nearly ripe human ovum in the living condition. The ovum is surrounded by a series of follicle cells (FC) in- side of which is the clear membrane (Hemb.) and within this is the ovum proper containing yolk granules (Y) and a nucleus (N) embedded in a clear mass of protoplasm. Magnified 500 diameters (x 500). (From O. Hertwig.) B, two human spermatozoa drawn to about the same scale of magnification. (After G. Retzius.) 12 HEREDITY AND ENVIRONMENT (b) Metabolism, or the transformation of matter and energy within the living thing, in the course of which some substances are oxi- dized into waste products, with the liberation of energy, while other substances are built up into protoplasm, each part of the cell con- verting food substances into its own particular substance by the process of assimilation. (c) Reproduction, or the capacity of organ- isms to give rise to new organisms, of cells to give rise to other cells, and of parts of cells to give rise to similar parts by the process of division. (d) Irritability, or the capacity of receiving and responding to impinging energies, or stimuli, in a manner which is usually, but not invariably, adaptive or useful. Both the egg and the sperm are living cells with typical cell structures and functions, but with none of the parts of the mature organism into which they may develop. But although they do not contain any of the differentiated structures and functions of the developed or- ganism, they differ from other cells in that they are capable under suitable conditions of FACTS AND FACTORS OF DEVELOPMENT 13 producing these structures and functions by the process of development or differentiation, in the course of which the general structures and functions of the germ cells are converted into the specific structures and functions of the mature animal or plant. In both plants and animals the sex cells are fundamentally alike, though they differ greatly in appearance. The female sex cells of flowering plants are called ovules, the male cells pollen. The corresponding cells of ani- mals are known as ova and spermatozoa. Col- lectively all kinds of sex cells are called gametes, and the individual formed by the union of a male and female gamete is known as a zygote, while the cell formed by the union of egg and sperm is frequently called the oosperm. The egg cell of animals is usually spherical in form and contains more or less food sub- stance in the form of yolk ; it varies greatly in size, depending chiefly upon the quantity of yolk, from the great egg of a bird, in which the yolk or egg proper may be hundreds of millimeters in diameter, to the miscroscopic 14 HEREDITY AND ENVIRONMENT eggs of oysters and worms, which may be no more than a few thousandths of a millimeter in diameter. The human ovum (Fig. 1) is microscopic in size (about 0.2 mm. in diameter) but it is not smaller than is found in many other animals. It has all the characteristic parts of any egg cell, and can not be distin- guished microscopically from the eggs of sev- eral other mammals, yet there is no doubt that the ova of each species differ from those of every other species, and later we shall see reasons for concluding that the ova produced by each individual are different from those produced by any other individual. The sperm, or male gamete, is among the smallest of all cells and is usually many thou- ... T ... M H A --'""" "****- ''' A _____ a* B FIG. 2. Two HUMAN SPERMATOZOA. A, showing the surface of the flattened head; B, its edge; H, head; M, middle-piece; T, tail. (After G. Retzius.) FACTS AND FACTORS OF DEVELOPMENT 15 sands of times smaller than the egg. In most animals, and in all vertebrates, it is an elongated, thread-like cell with an enlarged head which contains the nucleus, a smaller middle-piece, and a very long and slender tail or flagellum, by the lashing of which the sper- matozoon swims forward in the jerking fashion characteristic of many monads or flagellated protozoa. In different species of animals the spermatozoa often differ in size and appear- ance, and there is every reason to believe that the spermatozoa of each species are peculiar in certain respects even though we may not be able to distinguish any structural differences under the microscope. The human sperma- tozoa (Fig. 2) closely resemble those of other primates but are still slightly different, and the conclusion is logically inevitable, as we shall see later, that the spermatozoa as well as the ova of each individual differ slightly from those of every other individual. 2. Fertilization. If a spermatozoon in its swimming comes into contact with a ripe but unfertilized egg, the head and middle-piece of the sperm sink into the egg while the tail is 16 HEREDITY AND ENVIRONMENT usually broken off and left outside. The nucleus in the head of the sperm then begins to absorb material from the egg and to grow in size and at the same time a minute granule, the centrosome, appears, either from the mid- dle-piece or from the head of the sperm, and radiating lines run out from the centrosome into the substance of the egg. The sperm nucleus and centrosome then approach the egg nucleus and ultimately the two nuclei come to lie side by side (Figs. 4-7) . Usually when one spermatozoon has entered an egg all others are barred from entering, probably by some change in the chemical substances given out by the egg. This union of a single spermatozoon with an egg is known as fertilization. Whereas egg cells are usually, but not invariably, incapable of development without fertilization, there be- gins, immediately after fertilization, a long series of transformations and differentiations of the fertilized egg which leads to the develop- ment of a complex animal of a person. In the fusion of the egg and sperm a new indi- vidual, the oosperm, comes into being. The 5 . FIGS. 4-5. Two STAGES IN THE ENTRANCE OF THE SPERMATOZOON INTO THE EGG OF hereis. Some of the protoplasm of the egg has gath- ered at the point of entrance to form the entrance cone (EC) which, together with the sperm head, moves into the interior of the egg in later stages. The black spheres rep- resent yolk. (From F. R. Lillie.) FIG. 3. ENTIRE SPERMATOZOON OF THE ANNELID Nereis, showing perforatorium (P) ; head (H) ; middle-piece (M), and tail (T). (From F. R. Lillie.) 18 HEREDITY AND ENVIRONMENT oosperm, formed by the union of the two sex cells, is really a double cell, since parts of the egg and sperm never lose their identity, and the individual which develops from this oosperm is a double being; even in the adult man this double nature, caused by the union of egg and sperm, is never lost. In by far the larger number of animal species the oosperm, either just before or shortly after fertilization, is set free to begin its own individual existence, and in such cases it is perfectly clear that the fertilization of the egg marks the beginning of the new individual. But in practically every class of animals there are some species in which the fertilized egg is retained within the body of the mother for a varying period during which development is proceeding. In such cases it is not quite so evident that the new individual comes into be- ing with the fertilization of the egg; rather the moment of birth or the separation from the mother is generally looked upon as the be- ginning of the individual existence. And yet in all cases the egg or embryo is always dis- tinguishable from the body of the mother and FACTS AND FACTORS OF DEVELOPMENT 19 there is no protoplasmic connection between 'the two. In mammals generally, including also the human species, not a strand of proto- plasm, not a nerve fiber, not a blood vessel passes over from the mother to the embryo; the latter is from the moment of fertilization of the egg a distinct individual with particular individual characteristics, and this is just as true of viviparous animals in which the egg undergoes a part of its development within the body of the mother as it is of oviparous forms in which the eggs are laid before devel- opment begins. The fertilized egg of a star-fish, or frog, or man is not a different individual from the adults of these forms, rather it is a star-fish, a frog, or a human being in the one-celled stage, and thereafter this new being maintains its own individuality. This fertilized egg fuses with no other cells, it takes into itself no living substance, but manufactures its own proto- plasm from food substances; it receives food and oxygen from without and it gives out carbonic acid and other waste products; it is sensitive to certain alterations in the environ- lt Jfat. ^*=^'u- . *?^&&^ P'or description see opposite page. 1 st PB 9 FIGS. 6-9. SUCCESSIVE STAGES IN THE MATURATION AND FERTI- LIZATION OF THE EGG OF Nereis, less highly magnified than Figs. 6 and 7, showing the progress of the entrance cone (EC) and sperm nucleus (N) into the egg. Fig. 6 shows the first maturation spindle of the egg (1st Mat. Sp.) ; Fig. 7, the first polar body (1st PB) formed by this division; Fig. 8, the sec- ond maturation spindle (2d Mat. Sp.) and the sperm nucleus and spindle (cZV) ; Fig. 9, the division of the male and female nuclei in the first cleavage spindle (1st Cl. Sp.). (From F. R. Lillie.) 22 HEREDITY AND ENVIRONMENT ment such as thermal, chemical and electrical changes it is, in short, a distinct living thing, an individuality. Under proper environ- mental conditions this fertilized egg cell de- velops, step by step, without the addition of anything from the outside except food, water, oxygen, and such other raw materials as are necessary to the life of any adult animal, into the immensely complex body of a star-fish, a frog, or a man. At the same time, from the relatively simple reactions and activities of the fertilized egg there develop, step by step, without the addition of anything from without except raw materials and environmental stimuli, the multifarious activities, reactions, instincts, habits, and intelligence of the ma- ture animal. Is not this miracle of development more wonderful than any possible miracle of cre- ation? And yet as one watches this marvellous process by which the fertilized egg grows into the embryo, and this into the adult, each step appears relatively simple, each perceptible change is minute; but the changes are in- numerable and unceasing and in the end they FACTS AND FACTORS OF DEVELOPMENT accomplish this miracle of transforming the fertilized egg cell into the fish, or frog, or man a thing which would be incredible were it not for the fact that it has been seen by hundreds of observers and can be verified at any time by those who will take the trouble to study the process for themselves. A FIG. 10. FOUR STAGES IN THE CLEAVAGE OF THE EGG OF THE SHEEP; pb, polar bodies. (After Assheton.) 24 HEREDITY AND ENVIRONMENT 3. Cleavage. When the two germ nuclei, egg nucleus and sperm nucleus, have come into contact after the fertilization of the egg they divide by a complicated process known as mitosis, or indirect nuclear division (Fig. 9). The centrosome, which usually accompanies the sperm nucleus in its passage through the egg, divides and forms a spindle-shaped figure with astral radiations at its two poles (Figs. 7, 8). The chromatin, or stainable substance of the nucleus, takes the form of threads, the chromosomes ( Fig. 9 ) , of which there is a con- stant number for each species of animal and plant. Each chromosome then splits length- wise, its two halves moving to opposite ends of the spindle, in which position the daughter chromosomes fuse together to form the daugh- ter nuclei. In this way the chromatin of the egg and sperm nuclei is exactly halved. After the germ nuclei have divided in this manner the entire egg divides by a process of constriction into two cells (Figs. 10, 11 ). This is the beginning of a long series of cell divi- sions, each of them essentially like the first, by which the egg is subdivided successively into FIG. 11. SUCCESSIVE STAGES IN THE CLEAVAGE AND GASTRULA- TION OF Amphioxus. A, one cell; B, two cells; C and D, four cells; E, eight cells; F, sixteen cells; G, blastula stage of about ninety-six cells; H, section through the same showing the cleavage cavity; I, blastula seen from the left side showing three zones of cells, viz., an upper clear zone of ectoderm, a middle (faintly shaded) zone of mesoderm and a lower (deeply shaded) zone of endoderm cells; J, section through the same showing these three types of cells; K and L, successive stages in the infolding of the endoderm; cells indicated as in the pre- ceding figure. In all figures except D the polar body is shown at the upper pole. Figs. A-H after Hatschek. a, anterior; p, posterior; v, ventral; d, dorsal; be, blastocoel; gc, gastrocoel. 26 HEREDITY AND ENVIRONMENT a constantly increasing number of cells. Dur- ing the earlier divisions there is little or no in- crease in the volume of the egg, consequently successive generations of cells continually grow smaller (Figs. 10, 11). This process is known as the cleavage of the egg, and by it the egg is not only split up into a con- siderable number of small cells, but a much more important result is that the different kinds of protoplasm in the egg become isolated in different cleavage cells, so that these sub- stances can no longer freely commingle. The cleavage cells, in short, come to contain dif- ferent kinds of substance, and thus to differ from one another. The differentiations of the cleavage cells appear much earlier in some forms than in others, but in all cases such differentiations appear during cleavage. 4. Embryogeny. From this stage onward the course of development differs in different classes of animals to such an extent that it is difficult to formulate any general description which will apply to all of them. Usually the many cleavage cells form a hollow sphere, the blastula (Fig. 11, H), and this in turn be- FACTS AND FACTORS OF DEVELOPMENT 27 comes a gastrula (Fig. 11, K, L), in which at first two, and later three, groups or layers of cells may be recognized; the outer layer, which is formed from cells nearest the upper pole of the egg, is the ectoderm; the inner layer, or endoderm, is formed from cells near- est the lower pole; a middle layer, or group of cells, the mesoderm, is formed from cleav- age cells which in vertebrates lie between the upper and lower poles. FIG. 12, A and B. Two LATER STAGES IN THE DEVELOPMENT OF Amphioxus, showing the elongation of the embryo in the antero-posterior axis (a p), and formation of the somites (som) ; neural groove (ng) and neural tube (nt) ; ect, ecto- derm; mes, mesoderm; ac, alimentary canal. (After Hatschek.) 28 HEREDITY AND ENVIRONMENT 5. Organogeny. By further differentiation of the cells of these layers and by dissimilar growth and folding of the layers themselves the various organs of the embryo begin to ap- pear. From the ectoderm is formed the outer layer of the skin and the nervous system ; from the endoderm arise the lining of the aliment- ary canal and its outgrowths; from the meso- derm come, in whole or in part, the skeletal, muscular, vascular, excretory, and reproduc- tive systems. In vertebrates the nervous sys- -tem appears as a plate of rather large ecto- derm cells (Fig. 13 np) ; this plate rolls up at its sides to form a groove (Fig. 13 C) and then a tube (Fig. 13 D) ; and by enlarge- ment of certain portions of this tube and by foldings and thickenings of its walls the brain and spinal cord are formed (Fig. 15, C, D ) . The retina or sensory portion of the eye is formed as an outgrowth from the fore part of the brain (Fig. 15, D) ; the sensory portion of the ear comes from a cup-shaped depres- sion of the superficial ectoderm which covers the hinder portion of the head (Fig. 15, E and F) . The back-bone begins to appear as a deli- FACTS AND FACTORS OF DEVELOPMENT 29 cate cellular rod (Fig. 13, ch), which then in higher vertebrates becomes surrounded suc- cessively by a fibrous, a cartilaginous, and a bony sheath. And so one might go on with a description of all the organs of the body, each of which begins as a relatively simple group or layer of cells, which gradually become more complicated by a process of growth and dif- FIG. 13. CROSS SECTION OF Amphioxus LARVAE IN SUCCESSIVE STAGES OF DEVELOPMENT. A, through a larva similar to 11A; B and C, of a larva similar to 11B; D, of a still older larva; ect, ectoderm; ent, endoderm; mes, mesoderm; ch, notochord; np, neural plate; gc, gastrocoel; ac, alimentary canal; coel, coelom. 30 HEREDITY AND ENVIRONMENT ferentiation, until these embryonic organs as- sume more and more the mature form. 6. Oviparity and Viviparity. This very brief and general statement of the manner of embryonic development applies to all verte- brates, man included. There are many special features of human development which are treated at length in works on embryology, but which need not detain us here since they do not affect the general principles of develop- ment already outlined. In one regard the de- velopment of the human being or of any mam- mal is apparently very different from that of a bird or frog or fish, viz., in the fact that in the former the embryonic development takes place within the body of the mother whereas in the latter the eggs are laid before or soon after fertilization. In man, after the cleavage of the egg, a hollow vesicle is formed, which becomes attached to the uterine walls by means of processes or villi which grow out from it (Fig. 14, D, E, F) while only a small portion of the vesicle becomes transformed into the embryo. There is thus established a connection between the embryo and the uterine FACTS AND FACTORS OF DEVELOPMENT 31 FIG.. 14. DIAGRAMS SHOWING THE EARLY DEVELOPMENT OF THE HUMAN OOSPEHM. A, cleavage stage which has just come into the uterus; B and C, blastodermic vesicles embedded in the mucous membrane of the uterus; D, E and F, longitudinal sections of later stages, the anterior and posterior poles being marked by the axis a p. In C cavities have appeared in the ectoderm, entoderm and mesoderm. D, villi forming from the trophoblast (nutritive layer, tr) ; black indicates ectoderm (ect) ; oblique lines, entoderm; few stipples, mesoderm; V, villi; am, amnion; ys, yolk sac; n, neurenteric canal; x 25. (After Keibel.) 32 HEREDITY AND ENVIRONMENT walls through which nutriment is absorbed by the embryo. And yet this difference is not a fundamental one for in different animals there are all stages of transition between these two modes of development. While in most fishes, amphibians and reptiles the eggs are laid at the beginning of development and are free and independent during the whole course of ontogeny, there are certain species in each of these classes in which the development takes place within the body of the mother. Even in birds a portion of the development takes place within the body of the female before the eggs are laid, and there are mammals (mono- tremes) which lay eggs, while in others (mar- supials) the young are born in a very imperfect condition. These facts indicate that there is no fundamental difference between oviparity and viviparity. In the latter the union between the embryo and the mother is a nutritive but not a protoplasmic one. Blood plasma passes from one to the other by a process of soakage, and the only material influences which can affect the developing embryo are such as may be conveyed through the blood plasma and are FIG. 15. A-H, successive stages in the early development of the human embryo. A, blastodermic vesicle showing primitive axis in embryonic area; age unknown. B, blastodermic vesicle attached to uterine wall at the posterior pole, showing neural groove; age unknown. C, later stage in which the neural folds are closing and five pairs of somites have appeared; age, ten to fourteen days. D, stage of fourteen somites showing en- largements of the neural folds at the anterior end which will form the brain; age, fourteen to sixteen days. E and F later stages, the latter with twenty-three somites and three visceral clefts. The ear shows as a depression at the dorsal angle of the second cleft. O, embryo of thirty-five somites showing eye, branchial arches and limb buds. H, embryo of thirty-six somites showing nasal pit, eye, branchial arches and clefts, limb buds and heart. (After Keibel.) 34 HEREDITY AND ENVIRONMENT chiefly nutritive in character. Careful studies have shown that supposed "maternal impres- sions" of the physical, mental, or emotional conditions of the mother upon the unborn child have no existence in fact, except in so far as the quality of the mother's blood may be changed and may affect the child. At no time, whether before or after birth, is the mother more than nurse to the child. Hereditary in- fluences are transmitted only through the egg cell and the sperm cell and these influences are not affected by intra-uterine development. The principles of heredity and development are the same in oviparous and in viviparous animals in fishes, frogs, birds and men. Summary. This is a very brief and incom- plete statement of some of the important stages or phases of the development of the body of man or of any other vertebrate. In all cases development begins with the fertilized egg which contains none of the structures of the de- veloped animal, though it may exhibit the polarity and symmetry of the adult and may also contain specific kinds of protoplasm which will give rise to specific tissues or organs of FACTS AND FACTORS OF DEVELOPMENT 35 A B FIG. 16. A, human embryo of forty-two somites; age about twenty-one days. B, embryo of about four weeks. C, still older embryo showing the beginnings of the formation of digits. D, embryo of about two months. (After Keibel.) 36 HEREDITY AND ENVIRONMENT the adult. From this egg cell arise by divi- sion many cells which differ from one another more and more as development proceeds, until finally the adult animal results. A specific type of development is due to a specific organ- ization of the germ cells with which develop- ment begins, but the earlier differentiations of the egg are relatively few and simple as compared with the bewildering complexities of the adult, and the best way of understand- ing adult structures is to trace them back in development to their simpler beginnings and to study them in the process of becoming. 7. Development of Functions. The de- velopment of functions goes hand in hand with the development of structures; indeed function and structure are merely different aspects of one and the same thing, namely organization. All the general functions of living things are present in the germ cells, viz., (1) Constructive and destructive metabolism, (2) Reproduction, as shown in the division of cells and cell constituents, (3) Irritability, or the capacity of receiving and responding to stimuli. All these general functions of living FACTS AND FACTORS OF DEVELOPMENT 37 things are manifested by germ cells, but as de- velopment advances each of these functions be- comes more specialized, more complicated and more perfect. A cell which at an early stage was protective, locomotor and sensory in func- tion may give rise to daughter cells in which these functions are distributed to different cells; cells which at an early stage were sensi- tive to many kinds of stimuli give rise to daughter cells which are especially sensitive to one particular kind of stimulus, such as vi- bration, light, or chemicals. Functions develop from a generalized to a specialized condition by the process of "physi- ological division of labor" which accompanies morphological division of substance. But just as in the development of structures new parts, which were not present in the germ, appear by a process of "creative synthesis," so new func- tions appear in the course of development, which are not merely sorted out of the general functions present at the beginning, but whicli are created by the interaction and synthesis of parts and functions previously present. Much less attention has been paid to the de- 38 HEREDITY AND ENVIRONMENT velopment of functions than to the develop- ment of structures, and consequently it is not possible to describe the former with the same degree of detail as the latter. But in spite of the lack of detailed knowledge regarding the development of particular functions the gen- eral fact of such development is well estab- lished. To what extent structures may modify functions or functions structures, in the course of development, is a problem which has been much discussed, and upon the answer to it de- pends the fate of certain important theories, for example Lamarckism; but this problem can be solved only by thoroughgoing experi- mental and analytical work. In the meantime it seems safe to conclude that living structures and functions are inseparable and that any- thing which modifies one of these must of necessity modify the other also; they are merely different aspects of organization, and are dealt with separately by the morphologists and physiologists only as a matter of conven- ience. At the same time there can be no doubt that minute changes of function can frequently be detected where no corresponding change of FACTS AND FACTORS OF DEVELOPMENT 39 structure can be seen, but this shows only that physiological tests may be more delicate than morphological ones. In certain lines of mod- ern biological work, such as bacteriology, cytology, and genetics, many functional dis- tinctions are recognizable between organisms which are morphologically indistinguishable. But this does not signify that functional changes precede structural ones, but only that the latter are more difficult to see than the former. For every change of function it is probable that an "unlimited microscopist" could discover a corresponding change of structure. II. DEVELOPMENT or THE MIND The development of the mind parallels that of the body: whatever the ultimate relations of the mind and body may be, there can be no reasonable doubt that the two develop together from the germ. It is a curious fact that many people who are seriously disturbed by scientific teachings as to the evolution or gradual de- velopment of the human race accept with equanimity the universal observation as to the 40 HEREDITY AND ENVIRONMENT development of the human individual, mind as well as body. The animal ancestry of the race is surely no more disturbing to philosophi- cal and religious beliefs than the germinal origin of the individual, and yet the latter is a fact of universal observation which can not be relegated to the domain of hypothesis or theory, and which can not be successfully de- nied. If we admit the fact of the develop- ment of the entire individual, surely it matters little to our philosophical or religious beliefs to admit the development or evolution of the race. The origin of the mind, or rather of the soul, is a topic upon which there has been much speculation by philosophers and theologians. One of the earliest hypotheses was that which is known as transmigration or metempsychosis. This doctrine probably reached its greatest development in ancient India, where it formed an important part of Buddhistic belief; it was also a part of the religion of ancient Egypt; it was embodied in the philosophies of Pytha- goras and Plato. According to these teach- ings, the number of souls is a constant one; FACTS AND FACTORS OF DEVELOPMENT 41 souls are neither made nor destroyed, but at birth a soul which had once tenanted another body enters into the new body. This doctrine was generally repudiated by the Fathers of the Christian Church. Jerome and others adopted the view that God creates a new soul for each body that is generated, and that every soul is thus a special divine creation. This has become the prevailing view of the Christian Church and is known as creationism. On the other hand Tertullian taught that souls of children are generated from the souls of par- ents as bodies are 'from bodies. This doctrine, which is known as traducianism, has been de- fended by certain modern theologians, but has been formally condemned by the Roman Catholic Church. Traducianism undoubtedly comes nearer the scientific teachings as to the development of the mind than does either of the other doc- trines named, but it is based upon the preva- lent but erroneous belief that the bodies of the parents generate the body of the child, and that correspondingly the souls of the parents generate the soul of the child. Now we know 42 HEREDITY AND ENVIRONMENT that the child comes from germ cells which are not made by the bodies of the parents but have arisen by the division of antecedent germ cells. Every cell comes from a pre- existing cell by a process of division, and every germ cell comes from a pre-existing germ cell. Consequently it is not possible to hold that the body generates germ cells, nor that the soul generates souls. The only possible scientific position is that the mind (or soul) as well as the body develops from the germ. No fact in human experience is more certain than that the mind develops by gradual and natural processes from a simple condition which can scarcely be called mind at all; no fact in human experience is fraught with greater practical and philosophical significance than this, and yet no fact is more generally disregarded. We know that the greatest men of the race were once babies, embryos, germ cells, and that the greatest minds in human history were once the minds of babies, em- bryos and germ cells, and yet this stupendous fact has had but little influence on our beliefs as to the nature of man and of mind. We FACTS AND FACTORS OF DEVELOPMENT 43 rarely think of Plato and Aristotle, of Shake- speare and Newton, of Pasteur and Darwin, except in their full epiphany, and yet we know that when each of these was a child he "thought as a child and spake as a child," and when he was a germ cell he behaved as a germ cell. The development of the mind from the ac- tivities of the germ cells is certainly most won- derful and mysterious, but probably no more so than the development of the complicated body of the adult animal from the structures of the germ. Both belong to the same order of phenomena and there is no more reason for supposing that the mind is supernaturally created than that the body is. Indeed, we know that the mind is formed by a process of development, and the stages of this develop- ment are fairly well known. There is nowhere in the entire course of mental development a sudden appearance of psychical processes, but rather a gradual development of these from simpler and simpler beginnings. No detailed study has been made of the reactions of human germ cells and embryos, but there is every reason to believe that these reactions are 44 HEREDITY AND ENVIRONMENT simpler in the embryo and germ cell than in the infant, and that they are generally similar to the reactions of the germ cells and embryos of other animals, and to the behavior of many lower organisms. A few years ago such a statement would have been branded as "materialism" and promptly rejected without examination by those who are frightened by names. But the general spread of the scientific spirit is shown not only by the growing regard for evidence but also by the decreasing power of epithets. "Materialism," like many another ghost, fades away into thin air or at least loses many of its terrors, when closely scrutinized. But the statement that mind develops from the germ cells is not an affirmation of materialism, for while it identifies the origin of the entire indi- vidual, mind and body, with the development of the germ, it does not assert that "matter" is the cause of "mind" either in the germ or in the adult. It must not be forgotten that germ cells are living things and that we go no further in associating the beginnings of mind with the beginnings of body in the germ than FACTS AND FACTORS OF DEVELOPMENT 45 we do in associating mind and body in the adult. It is just as materialistic to hold that the mind of the mature man is associated with his body as it is to hold that the beginnings of mind in the germ are associated with the beginnings of the body, and both of these tenets are incontrovertible. It seems to me that the mind is related to the body as function is to structure; there are those who maintain that structure is the cause of function, that the real problem in evolution or development is the transformation of one structure into another, and that the functions which go with certain structures are merely incidental results ; on the other hand are those who maintain that function is the cause of structure and that the problem of evolution or development is the change which takes place in functions and habits, these changes causing corresponding transformations of structure. Among adherents of the former view may be classed many morphologists and Neo-Darwin- ians; among proponents of the latter, many physiologists and Neo-JLamarckians. It seems to me that the defenders of each of these views 46 HEREDITY AND ENVIRONMENT fail to recognize the essential unity of the en- tire organism, structure as well as function; that neither of these is the cause of the other, though each may modify or condition the other, but that they are two aspects of one common thing, viz., organization. In the same way I think that the body or brain is not the cause of mind, nor mind the cause of body or brain, but that both are inherent in one common or- ganization or individuality. In asserting that the mind develops from the germ as the body does, no attempt is made to explain the fundamental properties of body or mind. As the structures of the body may be traced back to certain fundamental struc- tures of the germ cell, so the characteristics of the mind may be traced back to certain funda- mental properties and activities of the germ. Many of the psychical processes may be traced back in their development to properties of sensitivity, reflex motions, and persistence of the effects of stimuli. All organisms manifest these properties and for aught we know to the contrary they may be original and neces- sary characteristics of living things. In the FACTS AND FACTORS OF DEVELOPMENT 47 simplest protoplasm we find organization, that is, structure and function, and in germinal protoplasm we find the elements of the mind as well as of the body, and the problem of the ultimate relation of the two is the same whether we consider the organism in its germi- nal or in its adult stage. In some way the mind as well as the body develops out of the germ. What are the germinal bases of mind? What are the psy- chical Anlagen in embryos and how do they develop? In this case, even more than in the development of the body, we are compelled to rely upon the comparison of human develop- ment with that of other animals, but the great principle of the oneness of life, as respects its fundamental processes, has never yet failed to hold true and will not fail us here. In the study of the psychical processes of organisms other than ourselves we are compelled to rely upon a study of their activities, their reactions to stimuli, since we can not approach the sub- ject in any other way. The reactions and be- havior of organisms under normal and experi- mental conditions give the only insight which 48 HEREDITY AND ENVIRONMENT we can get into their psychical processes; and this applies to men no less than to protozoa. 1. Sensitivity. The most fundamental phenomenon in the behavior of organisms is irritability or sensitivity, which is the capacity of receiving and responding to stimuli: this is one of the fundamental properties of all proto- plasm. But living matter is not equally sensi- tive to all stimuli, nor to all strengths of the same stimulus. Many of the simplest unicel- lular plants and animals show that they are differentially sensitive; they often move to- ward weak light and away from strong light, away from extremes of heat and cold, into certain chemical substances and away from others; in short, all organisms, even the sim- plest, may respond differently to different kinds of stimuli or to different degrees of the same stimulus. This is what is known as dif- ferential sensitivity (Figs. 17, 18, 19) . On the other hand, many organisms respond in the same way to different stimuli, and this may be taken to indicate generally that they are not differentially sensitive to such stimuli; it is FACTS AND FACTORS OF DEVELOPMENT 49 B C D E F 9 FIG. 17. DISTRIBUTION OF BACTERIA \~$ THE SPECTRUM. The largest group is in the ultra- red at the left; the next largest group is in the yellow-orange close to the line D. (From Jen- nings, after Engelmann.) not to be concluded because organisms respond differently to certain stimuli that they are therefore capable of distinguishing between all kinds of stimuli, for this is certainly not true. Even in adult men the capacity of dis- tinguishing between different kinds of stimuli is far from perfect. Egg cells and spermatozoa show this prop- erty of sensitivity. The egg is generally in- capable of locomotion, and since the results of stimulation must usually be detected by move- ments it is not easy to determine to what ex- tent the egg is sensitive; but though the egg lacks the power of locomotion, it possesses in a marked degree the power of intra-cellular movement of the cell contents. When a spermatozoon comes into contact with the sur- 50 HEREDITY AND ENVIRONMENT face of the egg the cortical protoplasm of the egg flows toward that point and may form a cone or protoplasmic prominence into which the sperm is received (Figs. 4, 5, EC). It is an interesting fact that the same sort of re- sponse follows when a frog's egg is pricked by a needle, thus showing that in this case the egg does not distinguish between the prick of the needle and that of the spermatozoon. The spermatozoon is usually a locomotor cell and it responds differently to certain stimuli, just as many bacteria and protozoa do; sper- matozoa are strongly stimulated by weak alkali and alcohol, they gather in certain chemical substances and not in others, they collect in great numbers around fertilizable egg cells, etc. The movements of fertilized egg cells, cleavage cells, and early embryonic cells are usually limited to flowing movements within the individual cells. These movements, which are of a complicated nature, are of the greatest significance in the differentiation of the egg into the embryo ; they are caused chiefly by in- ternal stimuli and by non-localized external FACTS AND FACTORS OF DEVELOPMENT 51 FIG. 18, a, b, c. REPULSION OF Spirilla BY COMMON SALT. a, condition immediately after adding crystals; b and c, later stages in the reaction. x, y, z, repulsion of Spirilla by distilled water. The upper drop consists of sea-water containing Spirilla, the lower drop, of distilled water. At x these have just been united by a narrow neck; at y and z, the bacteria have retreated before the distilled water. (From Jennings, after Massart.) 52 HEREDITY AND ENVIRONMENT ones. Modifications of the external stimuli often lead to modifications of these intra- cellular movements and to abnormal types of cleavage and development in short, these movements show that the fertilized egg is dif- ferentially sensitive. In the further course of development particular portions of the embryo become es- pecially sensitive to some kinds of stimuli, while other portions become sensitive to oth- ers. In this way the different sense organs, each especially sensitive to one particular kind of stimulus, arise from the generalized sensitivity of the oosperm, and thus general sensitivity, which is a property of all proto- plasm, becomes differential sensitivity and special senses in the process of embryonic dif- ferentiation. Such sensitivity is the basis of all psychic processes; sensations are the ele- ments of the mind. 2. Tropisms, Reflexes, Instincts. All the responses of germ cells, and of the simplest organisms, to stimuli are in the nature of trop- isms or reflexes, that is, relatively simple, automatic responses. Such tropisms or re- FACTS AND FACTORS OF DEVELOPMENT 53 flexes are seen in the movements of bacteria, protozoa and many higher animals and plants as well as in movements of spermatozoa, the movements of the protoplasm in egg cells and embryonic cells, the movements of cells and 19* 19* 26* f 38 10 25~ FIG. 19. REACTIONS OF Paramecium TO HEAT AND COLD. At a the infusoria are uniformly distributed in a trough, both ends of which have a temperature of 19; at 6 the infusoria are shown collected at the cooler end of the trough; at c they have collected at the warmer end of the trough. (From Jen- nings, after Mendelssohn.) 54 HEREDITY AND ENVIRONMENT cell masses in the formation of the gastrula, alimentary canal, nervous system and other organs. Indeed the entire process of develop- ment, whether accompanied by visible move- ments or not, may be regarded as a series of automatic responses to stimuli. When the embryo becomes differentiated to such an extent as to have specialized organs for producing movement its capacity for mak- ing responsive movements to stimuli becomes much increased. If the responses of animals and plants to stimuli are of such a sort that the organism turns or moves toward or away from a source of stimulus they are termed tropisms; if the responses are very compli- cated, one response calling forth another and involving many reflexes, as is frequently the case in animals, they are known as instincts. In the embryo the rhythmic contractions of heart, amnion and intestine are early manifes- tations of reflex motions. These appear chiefly in the involuntary muscles before nervous con- nections are formed, the protoplasm of the muscle cells probably responding directly to the chemical stimulus of certain salts in the FACTS AND FACTORS OF DEVELOPMENT 55 body fluids, as Loeb has shown in other cases. Reflexes which appear later are the random movements of the voluntary muscles of limbs and body, which are called forth by nerve im- pulses. Tropisms are manifested only by or- ganisms capable of considerable free movement and hence are absent in the foetus though present in many free living larvae Some in- stincts are present immediately after birth, such as the instinct of sucking or crying, though these are so simple when compared with some instincts which develop later that they might be classed as reflexes ; it is doubtful whether any of the activities before birth could properly be designated as instincts. Reflexes, tropisms and instincts have had a phylogenetic as well as an ontogenetic origin, and conse- quently we might expect that they would in general make for the preservation of the species, and as a matter of fact we usually find that they are remarkably adapted to this end. For instance the instincts of the human infant to grasp objects, to suck things which it can get into its mouth, to cry when in pain, are complicated reflexes which have survived in 56 HEREDITY AND ENVIRONMENT the course of evolution probably because they serve a useful purpose. Very much has been written on the nature and origin of instincts, but the best available evidence strongly favors the view that instincts are complex reflexes, which, like the structures of an organism, have been built up, both onto- genetically and phylogenetically, under the stress of the elimination of the unfit, so that they are usually adaptive. 3. Memory. Another general character- istic of protoplasm is the capacity of storing up or registering the effects of previous stimuli. A single stimulus may produce changes in an organism which persist for a longer or shorter time, and if a second stimulus occurs while the effect of a previous one still persists, the response to the second stimulus may be very different from that to the first. Macf arlane found that if the sensitive hairs on the leaf of Dionaea, the Venus fly-trap (Fig. 20, SH), be stroked once no visible response is called forth, but if they be stroked a second time within three minutes the leaf instantly closes. If a longer period than three minutes FACTS AND FACTORS OF DEVELOPMENT 57 elapses after the first stimulus and before the second no visible response follows, i. e. } two successive stimuli are necessary to cause the leaves to close, and the two must not be more than three minutes apart; the effects of the first stimulus are in some way stored or regis- tered in the leaf for this brief time. This kind of phenomenon is widespread among living things and is known as "summation of stim- uli." In all such cases the effects of a former stimulus are in some way stored up for a longer or shorter time in the protoplasm. It is possible that this is the result of the forma- tion of some chemical substance which remains in the protoplasm for a certain time, during which time the effects of the stimulus are said to persist, or it may be due to some physical change in the protoplasm analogous to the "set" in metals which have been subjected to mechanical strain. Probably of a similar character is the per- sistence of the effects of repeated stimuli and responses on any organ of a higher animal. A muscle which has contracted many times in a definite way ultimately becomes "trained" so 58 HEREDITY AND ENVIRONMENT that it responds more rapidly and more ac- curately than an untrained muscle; and the nervous mechanism through which the stimu- lus is transmitted also becomes trained in the same way. Indeed such training is probably chiefly a training of the nervous mechanism. The skill of the pianist, of the tennis player, of the person who has learned the difficult art FIG. 20. Dionaea muscipula (VENUS' FLY-THAP). Three leaves showing marginal teeth and sensitive hairs (SH). The leaf at the left is fully expanded, the one at the right is closed. PACTS AND FACTORS OF DEVELOPMENT 59 of standing and walking, or the still more diffi- cult art of talking, is probably due to the per- sistence in muscles and nerves of the effects of many previous activities. All such phe- nomena were called by Hering "organic memory," to indicate that this persistence of the effects of previous activities in muscles and other organs is akin to that persistence of the effects of previous experiences in the nervous mechanism which we commonly call memory. It seems probable that this ability of proto- plasm in general to preserve for a time the effects of former stimuli is fundamentally of the same nature as the much greater power of nerve cells to preserve such effects for much longer periods and in complex associations, a faculty which is known as associative memory. The embryos, and indeed even the germ cells of higher animals, may safely be assumed to be endowed with protoplasmic and organic memory, out of which, in all probability, de- velop associative and conscious memory in the mature organism. 4. Intellect, Reason. Even the intellect and reason which so strongly characterize man 60 HEREDITY AND ENVIRONMENT have had a development from relatively simple beginnings. All children come gradually to an age of intelligence and reason. In its simpler forms at least reason may be defined as the power of predicting future events and of reaching conclusions regarding unexperi- enced phenomena under the influence of past experience. In the absence of individual ex- perience young children have none of this power, but it comes gradually as a result of remembering past experiences and of fitting such experiences into new conditions. Young infants and many lower animals lack the power of reason, though their behavior is fre- quently of such a sort as to suggest that they are reasoning. Even the lowest animals avoid injurious substances and conditions and find beneficial ones; more complex animals learn to move objects, solve problems, and find their way through labyrinths in the shortest and most economical way; but this apparently in- telligent and purposive behavior has been shown to be due to the general elimination of all sorts of useless activities, and to the per- sistence of the useful ones. FACTS AND FACTORS OF DEVELOPMENT 61 The ciliated infusorian, Paramedum, moves by the beating of cilia which are arranged in such a way that they drive the animal forward in a spiral course. However, when it is strongly irritated, the normal forward move- ment is reversed ; the cilia beat forward instead of backward and the animal is driven back- ward for some distance (Fig. 21, 1, 2, 3) ; it then stands nearly still, merely rolling over and swerving toward the aboral side, and finally it goes ahead again, usually on a new course (Fig. 21, 3, 4, 5, 6). These move- ments seem to be conditioned rather rigidly by the organization of the animal: they are more or less fixed and mechanical in character, though to a certain extent they may be modi- fied by experience or physiological states. Paramedum behaves as it does in virtue of its constitution, just as an egg develops in a particular way because of its particular organization. But although limited in its behavior to these relatively simple motor reactions, Paramedum does many things which seem to show intelli- gence and purpose. It avoids many injurious 62 HEREDITY AND ENVIRONMENT substances, such as strong salts or acids, and it collects in non-injurious or beneficial sub- stances, such as weak acids, masses of bacteria upon which it feeds, etc. It avoids extremes of heat and cold and if one end of a dish con- taining Paramecia is heated and the other end is cooled by ice, the Paramecia collect in the region somewhere between these two extremes (Fig. 19). Jennings, by studying carefully the behavior of single individuals, established the fact that this apparently intelligent action is due to differential sensitivity and to the single motor reaction of the animal. If in the FIG. 21. DIAGRAM OF THE AVOIDING REACTION OF Parame- cium. A is a solid object or other source of stimulation. 1-6, successive positions occupied by the animal. The rotation on the long axis is not shown. (After Jennings.) FACTS AND FACTORS OF DEVELOPMENT 63 course of its swimming a Paramecium comes into contact with an irritating substance or condition, it backs a short distance, swerves toward its aboral side, and goes ahead in a new path ; if it again comes in contact with the irritating conditions this reaction is repeated, and so on indefinitely until finally a path is found in which the source of irritation is avoided altogether. In short, Paramecium continually tries its environment, and backs away from irritating substances or conditions. Its apparently intelligent reactions are thus explained as due to a process of "trial and error." 1 The behavior of worms, star-fishes, crusta- ceans, mollusks, as well as of fishes, frogs, 1 In Paramecium, there is certainly no consciousness of trial and error, and probably no unconscious attempt on the part of the animal to attain certain ends. Its responses are reflexes or tropisms, which are determined by the nature of the animal and the character of the stimulus. The fact that these re- sponses are in the main self-preservative is due to the teleo- logical organization of Paramecium which has been evolved, according to current opinion, as the result of long ages of the elimination of the unfit. If, in the opinion of any one, the expression "trial and error" necessarily involves a striving after ends, it would be advisable to replace it in this case by some such term as "useful or adaptive reactions." 64 HEREDITY AND ENVIRONMENT reptiles, birds and mammals, has been studied and in all cases it is found that their method of responding to stimuli is not at first really purposive and intelligent but by the gradual elimination of useless responses and the preservation (or remembering) of useful ones the behavior may come to be purposive and intelligent. Thorndike found that when dogs, cats and monkeys were confined in cages which could be opened from the inside by turning a button, or pressing upon a lever, or pulling a cord, they at first clawed around all sides of the cage until by chance they happened to operate the mechanism which opened the door. There- after they gradually learned by experience, that is, by trial and error, and finally by trial and success, just where and how to claw in order to get out at once. When a dog has learned to turn a button at once and open a door we say he is intelligent, and if he can learn to apply his knowledge of any particular cage to other and different cages, a thing which Thorndike denies, we should be justified in saying that he reasons, though in this case FACTS AND FACTORS OF DEVELOPMENT 65 intelligence and reason are founded upon memory of many past experiences, of many trials and errors and of a few trials and successes. There is every evidence that human beings arrive at intelligence and reason by the same process, a process of many trials and errors and a few trials and successes, a remembering of these past experiences and an application of them to new conditions. A baby grasps for things which are out of its reach, until it has learned by experience to appreciate distances; it tests all sorts of pleasant and unpleasant things until it has learned to avoid the latter and seek the former; it experiments with its own body until it has learned what it can do and what it can not do. Is not this learning by experience akin to the same process in the dog and more remotely to the trial and error of the earthworm or the adaptive reflexes of Paramecium? Is not intelligence and reason in all of us, and upon all subjects, based upon the same processes of trial and error, memory of past experiences and application of this to new conditions? Surely this is true in all ex- 66 HEREDITY AND ENVIRONMENT perimental and scientific work. Indeed the scientific method is the method of trial and error, and finally trial and success the method recommended by St. Paul to prove all things and hold fast that which is good. In Paramecium the reflex type of behavior is relatively complete; there is no associative memory and no ability to learn by experience. In the earthworm associative memory is but slightly developed and the animal learns but little by experience and can make no applica- tion of past experiences to new conditions. In the dog associative memory is well developed; the animal learns by experience and can, to a limited extent, apply such memory of past ex- periences to new conditions. In adult man all of these processes are fully developed and par- ticularly the last, viz., the ability to reason. But in his development the human individual passes through the more primitive stages of intelligence, represented by the lower animals named; the germ cells and embryo represent only the stages of reflex behavior, to these trial and error and associative memory are added in the infant and young child, and to these the FACTS AND FACTORS OF DEVELOPMENT 67 application of past experience to new condi- tions, or reason, is added in later years. 5. Will. Another characteristic, which many persons regard as the supreme psychical faculty, is the will. This faculty also under- goes development and from relatively simple beginnings. The will of the child has devel- oped out of something which is far less perfect in the infant and embryo than in the child. Observations and experiments on lower ani- mals and on human beings, as well as intro- spective study of our own activities, appear to justify the following conclusions: (1.) Every activity of an organism is a response to one or more stimuli, external or internal in origin. These stimuli are in the main, if not entirely, energy changes outside or inside the organism. In lower organisms as well as in the germ cells and embryos of higher animals the possible number of re- sponses are few and prescribed owing to their relative simplicity, and the response follows the stimulus directly. In more complex or- ganisms the number of possible responses to a stimulus is greatly increased, and the visible 68 HEREDITY AND ENVIRONMENT response may be the end of a long series of internal changes which are started by the original stimulus. (2.) The response to a stimulus may be modified or inhibited in the following ways: (a) Through conflicting stimuli and changed physiological states, due to fatigue, hunger, etc. Many stimuli may reach the organism at the same time and if they conflict they may nullify one another or the organism may respond to the strongest stimulus and disregard the weaker ones. When an organ- ism has begun to respond to one stimulus it is not easily diverted to another. Jennings found that the attached infusorian, Stentor, which usually responds to strong stimuli by closing up, may, when repeatedly stimulated, loosen its attachment and swim away, thus respond- ing in a wholly new manner when its physi- ological state has been changed by repeated stimuli and responses. Whitman found that leeches of the genus Clepsine prefer shade to bright light, and other things being equal they always seek the under sides of stones and shaded places ; but if a turtle from which they FACTS AND FACTORS OF DEVELOPMENT 69 normally suck blood is put into an aquarium with the leeches, they at once leave the shade and attach themselves to the turtle. They prefer shade to bright light but they prefer their food to the shade. The tendency to re- main concealed is inhibited by the stronger stimulus of hunger. On the other hand he found that the salamander, Necturus, is so timid that it will not take food, even though starving, until by gradual stages and gentle treatment its timidity can be overcome to a certain extent. Here fear is at first a stronger stimulus than hunger and unless the stimulus of fear can be reduced the animal will starve to death in the presence of the most tempting food. (b) Responses may also be modified through compulsory limitation of many pos- sible responses to a particular one, and the con- sequent formation of a habit. This is the method of education employed in training all sorts of animals. Thus Jennings found that a star-fish could be trained to turn itself over, when placed on its back, by means of one par- ticular arm simply by persistently preventing 70 HEREDITY AND ENVIRONMENT the use of the other arms. Many responses of organisms are modified in a similar way, not only by artificial limitations but also by natural ones. (c) Responses which have become fixed and constant through natural selection or other means of limitation may become more varied and general when the compulsory limitation is relaxed. Behavior in the former case is fixed and instinctive, in the latter more varied and plastic. Thus Whitman found that the be- havior of domesticated pigeons is more vari- able and their instincts less rigidly fixed than in wild species. If the eggs are removed to a little distance from the nest the wild passenger pigeon returns to the nest and sits down as if nothing had happened. She soon finds out, not by sight but by feeling, that something is missing, and she leaves the nest after a few minutes without heeding the eggs. The ring- neck pigeon also misses the eggs and some- times rolls one of them back into the nest, but never attempts to recover more than one. The dove-cote pigeon generally tries to recover both eggs. According to Whitman: FACTS AND FACTORS OF DEVELOPMENT 71 In these three grades the advance is from extreme blind uniformity of action, with little or no choice, to a stage of less rigid uniformity. . . . Under con- ditions of domestication the action of natural selec- tion has been relaxed, with the result that the rigor of instinctive co-ordination, which bars alternative action, is more or less reduced. Not only is the door to choice thus unlocked, but more varied opportuni- ties and provocations arise, and thus the internal mechanism and the external conditions and stimuli work both in the same direction to favor greater freedom of action. When choice thus enters no new factor is introduced. There is greater plasticity within and more provocation without, and hence the same bird, without the addition or loss of a single nerve cell, becomes capable of higher action and is encouraged and even constrained by circumstances to learn to use its privileges of choice. Choice, as I conceive it, is not introduced as a little deity en- capsuled in the brain. . . . But increased plasticity invites greater interaction of stimuli and gives more even chances for conflicting impulses. (d) Finally in all animals behavior is modi- fied through previous experience, just as structure is also. Where several responses to a stimulus are possible and where experience has taught that one response is more satisfactory than another, action may be limited to this particular response, not by external compul- 72 HEREDITY AND ENVIRONMENT sion but by the internal impulse of experience and intelligence. This is what we know as conscious choice or will. Whitman says: Choice runs on blindly at first and ceases to be blind only in proportion as the animal learns through nature's system of compulsory education. The tele- ological alternatives are organically provided; one is taken and fails to give satisfaction, another is tried and gives contentment. This little freedom is the dawning grace of a new dispensation, in which educa- tion by experience comes in as an amelioration of the law of elimination. . . . Intelligence implies varying degrees of freedom of choice, but never complete emancipation from automatism. Freedom of action does not mean action without stimuli, but rather the introduction of the results of experience and intelligence as additional stimuli. The activities which in lower animals are "cabined, cribbed, confined," reach in man their fullest and freest expres- sion; but the enormous difference between the relatively fixed behavior of a protozoan or a germ cell and the relatively free activities of a mature man is bridged not only in the proc- ess of evolution, but also in the course of indi- vidual development. FACTS AND FACTORS OF DEVELOPMENT 73 6. Consciousness. The most complex of all psychic phenomena, indeed the one which includes many if not all of the others, is con- sciousness. Like every other psychic process this has undergone development in each of us ; we not only came out of a state of unconscious- ness, but through several years we were grad- ually acquiring consciousness by a process of development. Whether consciousness is the sum of all the psychic faculties, or is a new product dependent upon the interaction of the other faculties, it must pass through many stages in the course of its development, stages which would commonly be counted as uncon- scious or subconscious states, and complete consciousness must depend upon the complete development and activity of the other facul- ties, particularly associative memory and in- telligence. The question is sometimes asked whether germ cells, and indeed all living things, may not be conscious in some vague manner. One might as well ask whether water is present in hydrogen and oxygen. Doubtless the elements out of which consciousness de- velops are present in the germ cells, in the 74 HEREDITY AND ENVIRONMENT same sense that the elements of the other psychic processes or of the organs of the body are there present; not as a miniature of the adult condition, but rather in the form of ele- ments or factors, which by a long series of combinations and transformations, due to in- teractions with one another and with the en- vironment, give rise to the fully developed condition. Finally there seems good reason for believ- ing that the continuity of consciousness, the continuing sense of identity, is associated with the continuity of material substance, for in spite of frequent changes of the materials of which we are composed our sense of identity remains undisturbed. However, the contin- uity of protoplasmic and cellular organization generally remains undisturbed throughout life, and the continuity of consciousness is asso- ciated with this continuity of organization, especially in certain parts of the brain. It is an interesting fact that in man, and in several other animals which may be assumed to have a sense of identity, the nerve cells, especially those of the brain, cease dividing at an early FACTS AND FACTORS OF DEVELOPMENT 75 age, and these identical cells persist through- out the remainder of life. If nerve cells con- tinued to divide throughout life, as epithelial cells do, there would be no such persistence of identical cells, and one is free to speculate that in such cases there would be no persis- tence of the sense of identity. Organization includes both, structure and function, and continuity of organization im- plies not only persistence of protoplasmic and cellular structures but also persistence of the functions of sensitivity, reflexes, memory, in- stincts, intelligence, and will ; the continuity of consciousness is associated with the continuity of these activities, as well as with the struc- tures of the body in general and of the brain in particular. It is well known that things which interrupt or destroy these functions or struc- tures interrupt or destroy consciousness. Lack of oxygen, anesthetics, normal sleep cause in some way a temporary interruption of these functions and consequently tempo- rary loss of consciousness; while certain in- juries or diseases of the brain which bring about the destruction of certain centers or as- 76 HEREDITY AND ENVIRONMENT sociation tracts may cause permanent loss of consciousness. The development of all of these psychical faculties runs parallel with the development of bodily structures and apparently the method of development in the two cases is similar, viz., progressive differentiation of complex and specialized structures and func- tions from relatively simple and generalized beginnings. Indeed the entire organism, structure and function, body and mind, is a unity, and the only justification for dealing with these constituents of the organism as if they were separate entities, whether they be regarded in their adult condition or in the course of their development, is to be found in the increased convenience and effectiveness of such separate treatment. Development, like many other vital phe- nomena, may be considered from several dif- ferent points of view, such as (1) physico- chemical events involved, (2) physiological processes, (3) morphological characters, (4) ecological correlations and adaptations, (5) psychological phenomena, (6) social and FACTS AND FACTORS OF DEVELOPMENT 77 moral developments. All of these phases of development are correlated, indeed they are parts of one general process, and a complete account of this process must include them all. General considerations may lead us to the be- lief that each of the succeeding aspects of de- velopment named above may be causally ex- plained in terms of the preceding ones, and hence all be reducible to physics and chemistry. But this is not now demonstrable and may not be true. Function and structure may be related causally, or they may be two aspects of one substance. The same is true of body and mind or of matter and energy. But even if each of these different phases in the develop- ment of personality may not be causally ex- plained by the preceding ones, at least the principle of explanation employed for any aspect of development ought to be consistent and harmonious with that employed for any other aspect. The phenomena of mental development in man and other animals may be summarized as follows : 78 HEREDITY AND ENVIRONMENT DEVELOPMENT OF PSYCHICAL PROCESSES IN ONTO- GENY AND PHYLOGENY ALL LIVING THINGS, IN- CLUDING GERM CELLS AND EMBRYOS, SHOW: 1. Differential Sensitivity = Different Responses to Stimuli differing in Kind or Quantity. 2. Reflex Motions Relatively Simple, Auto- matic Responses. 3. Organic Memory = Results of Previous Ex- perience registered in General Protoplasm. 4. Adaptive Responses = Results of Elimination of Useless Responses through Trial and Error. 5. Varied Responses Dependent upon Conflict- ing Stimuli and Physi- ological States. 6. Identity =: Continuity of Individual Organization. MATURE FORMS OF HIGHER ANIMALS SHOW: 1. Special Senses and Sen- sations Sensations are the Ele- . ments of Mind. 2. Instincts (Inherited), Habits (Acquired) = Complex Reflexes, involv- ing Nerve Centers. 3. Associative Memory Results of Experience registered in Nerve Cen- ters and Association Tracts. 4. Intelligence, Reason =. Results of Trial and Er- ror plus Associative Memory, i. e. Experi- ence. 5. Inhibition, Choice, Will Dependent upon Associa- tive Memory, Intelli- gence, Reason. 6. Consciousness = Continuity of Memory, Intelligence, Reason, Will. FACTS AND FACTORS OF DEVELOPMENT 79 B. FACTORS OF DEVELOPMENT These are some of the facts of development, a very incomplete resume of some of the stages through which a human being passes in the course of his development from the germ. What are the factors of development? By what processes is it possible to derive from a relatively simple germ cell the complexities of an adult animal? How can mind and con- sciousness develop out of the relatively simple psychical elements of the germ? These are some of the great problems of development the greatest and most far-reaching theme which has ever occupied the minds of men. 1. Preformation. When the mind is once lost in the mystery of this ever-recurring mira- cle it is not surprising to find that there have been those who have refused to believe it possible and who have practically denied de- velopment altogether. The old doctrine of "evolution," as it was called by the scientists of the eighteenth century, or of preformation as we know it to-day, held that all the organs or 80 HEREDITY AND ENVIRONMENT parts of the adult were present in the germ in a minute and transparent condition as the leaves and stem are present in a bud, or as the shoot and root of the little plant are present in the seed. 2 In the case of animals it was generally impossible to see the parts of the future animal in the germ, but this was sup- posed to be due to the smaller size of the parts and to their greater transparency, and with poor microscopes and good imagination some observers thought they could see the little ani- mals in the egg or sperm, and even the little man, or "homunculus," was described and figured as folded up in one or the other of the sex cells. This doctrine of preformation was not only an attempt to solve the mystery of develop- ment, but it was also an attempt to avoid the theological difficulties supposed to be involved in the view that individuals are produced by a process of gradual development rather than 'The little plant in the seed is itself the product of the de- velopment of a single cell, the ovule, in which no trace of a plant is present, but of course this fact was not known until after careful microscopical studies had been made of the earliest stages of development. FACTS AND FACTORS OF DEVELOPMENT 81 by supernatural creation. If every individual of the race existed within the germ cells of the first parents, then in the creation of the first parents the entire race with its millions of in- dividuals was created at once. Thus arose the theory of "emboitement," or infinite encase- ment, the absurdities of which contributed to the downfall of the entire doctrine of prefor- mation, which, in the form given it by many naturalists of the eighteenth century, is now only a curiosity of biological literature. 2. Epigenesis. As opposed to this doctrine of preformation, which was founded largely on speculation, arose the theory of epigenesis, which was in its main features founded upon the direct observation of development, and which maintained that the germ contains none of the adult parts, but that it is absolutely simple and undifferentiated, and that from these simple beginnings the individual grad- ually becomes complex by a process of differ- entiation. We owe the theory of epigenesis, at least so far as its main features are con- cerned, to William Harvey, the discoverer of the circulation of the blood, and to Caspar 82 HEREDITY AND ENVIRONMENT Friederich Wolff, whose doctoral thesis, pub- lished in 1759 and entitled "Tlieoria Genera- tionis" marked the beginning of a great epoch in the study of development. Wolff demon- strated that adult parts are not present in the germ, either in animals or in plants, but that these parts gradually appear in the process of development. He held, erroneously, that the germ is absolutely simple, homogeneous and undifferentiated, and that differentiation and organization gradually appear in this undiffer- entiated substance. How to get differentia- tions out of non-differentiated material, heterogeneity out of homogeneity, was the great problem which confronted Wolff and his followers, and they were compelled to assume some extrinsic or environmental force, some vis formativia or spiritus rector, which could set in motion and direct the process of development. The doctrine of preformation, by locating in the germ all the parts which would ever arise from it, practically denied development altogether; epigenesis recognized the fact of development, but attributed it to mysterious FACTS AND FACTORS OF DEVELOPMENT 83 and purely hypothetical external forces; the one placed all emphasis upon the germ and its structures, the other upon outside forces and conditions. 3. Preformation and Epigenesis. Modern students of development recognize that neither of these extreme views is true adult parts are not present in the germ, nor is the latter homogeneous but there are in germ cells many different structures and functions which are, however, very unlike those of the adult, and by the transformation and differentiation of this germinal organization the complicated organization of the adult arises. Development is not the unfolding of an infolded organism, nor the mere sorting of materials already pres- ent in the germ cells, though this does take place, but rather it consists in the formation of new materials and qualities, of new struc- tures and functions by the combination and interaction of the germinal elements present in the oosperm. In similar manner the combina- tion and interaction of chemical elements yield new substances and qualities which are not to be observed in the elements themselves. Such 84 HEREDITY AND ENVIRONMENT new substances and qualities, whether in the organic or in the inorganic world, do not arise by the gradual unfolding of what was present from the beginning, but they are produced by a process of "creative synthesis." Modern studies of germ cells have shown that they are much more complex than was formerly believed to be the case; they may even contain different "organ-forming sub- stances" which in the course of development give rise to particular organs ; these substances may be so placed in the egg as to foreshadow the polarity, symmetry and pattern of the embryo, but even the most highly organized egg is relatively simple as compared with the animal into which it ultimately develops. In- creasing complexity, which is the essence of development, is caused by the combination and interaction of germinal substances under the influence of the environment. The organiza- tion of the oosperm may be compared to the arrangement of tubes and flasks in a compli- cated chemical operation ; they stand in a defi- nite relation to one another and each contains specific substances. The final result of the FACTS AND FACTORS OF DEVELOPMENT 85 operation depends not merely upon the sub- stances used, nor merely upon the way in which the apparatus is set up, but upon both of these things, as well as upon the environmental con- ditions represented by temperature, pressure, moisture or other extrinsic factors. 4. Heredity and Environment. Unques- tionably the factors or causes of development are to be found not merely in the germ but also in the environment, not only in intrinsic but also in extrinsic forces; but it is equally certain that the directing and guiding factors of development are in the main intrinsic, and are present in the organization of the germ cells, while the environmental factors exercise chiefly a stimulating, inhibiting or modifying influence on development. In the same dish and under similar environmental conditions, one egg will develop into a worm, another into a sea urchin, another into a fish, and it is cer- tain that the different fate of each egg is de- termined by conditions intrinsic in the egg itself, rather than by environmental conditions. We should look upon the germ as a living thing, and upon development as one of its 86 HEREDITY AND ENVIRONMENT functions. Just as the character of any func- tion is determined by the organism, though it may be modified by environment, so the char- acter of development is determined by hered- ity, t . e., by the organization of the germ cells, though the course and results of develop- ment may be modified by .environmental conditions. SUMMARY In conclusion, we have briefly reviewed in this lecture the well known fact that every liv- ing thing in the world has come into existence by a process of development; that the entire human personality, mind as well as body, has thus arisen; and that the factors of develop- ment may be classified as intrinsic in the or- ganization of the germ cells, and extrinsic as represented in environmental forces and con- ditions. The intrinsic factors are those which are commonly called heredity, and they direct and guide development in the main; the ex- trinsic or environmental factors furnish the conditions in which development takes place and modify, more or less, its course. CHAPTER II THE CELLULAR BASIS OF HERED- ITY AND DEVELOPMENT CHAPTER II THE CELLULAR BASIS OF HEREDITY AND DEVELOPMENT A. INTRODUCTORY Heredity is to-day the central problem of biology. This problem may be approached from many sides, that of the observer, the statistician, the practical breeder, the experi- menter, the embryologist, the cytologist; but these different aspects of the subject may be reduced to three general methods of study, (1) the observational and statistical, (2) the experimental, (3) the cytological and embry- ological. Before taking up these different as- pects of heredity it is important that we should have clear definitions of the terms employed and a fairly accurate conception of the pro- cesses involved. 1. Definitions. Heredity originally meant 89 90 HEREDITY AND ENVIRONMENT heirship, or the transmission of property from parents to children, and in the field of biology it has been defined erroneously as "the trans- mission of qualities or characteristics, mental or physical, from parents to offspring" (Cen- tury Dictionary). The colloquial meaning of the word has led to much confusion in biology, for it carries with it the idea of the transmis- sion from one generation to the next of owner- ship in property. A son may inherit a house from his father and a farm from his mother, the house and farm remaining the same though the ownership has passed from parents to son. And when it is said that a son inherits his stature from his father and his complexion from his mother, the stature and complexion are usually thought of only in their developed condition, while the great fact of development is temporarily forgotten. Of course there are no "qualities" or "characteristics" which are "transmitted" as such from one generation to the next. Such terms are not without fault when used merely as figures of speech, but when interpreted literally, as they frequently are, they are altogether misleading; they are THE CELLULAR BASIS 91 the result of reasoning about names rather than facts, of getting far from phenomena and philosophizing about them. The compari- son of heredity to the transmission of property from parents to children has produced con- fusion in the scientific as well as in the popu- lar mind. It is only necessary to recall the most elementary facts about development to recognize that in a literal sense developed char- acteristics of parents are never transmitted to children. 2. The Transmission Hypothesis. And yet the idea that the characteristics of adult persons are transmitted from one generation to the next is a very ancient one and was uni- versally held until the most recent times. Be- fore the details of development were known it was natural to suppose, as Hippocrates did, that white-flowered plants gave rise to white- flowered seeds and that blue-eyed parents pro- duced blue-eyed germs, without attempting to define what was meant by white-flowered seed or blue-eyed germs. And even after the facts of development were fairly well known it was generally held that the germ cells were pro- 92 HEREDITY AND ENVIRONMENT duced by the adult animal or plant and that the characteristics of the adult were in some way carried over to the germ cells; but the manner in which this supposed transmission took place remained undefined until Darwin attempted to explain it by his "provisional hypothesis of pangenesis." Darwin assumed that minute particles or "gemmules" were given off by every cell of the body, at every stage of development, and that these gem- mules then collected in the germ cells which thus became storehouses of little germs from all parts of the body. Afterward, in the de- velopment of the germ cells, the gemmules, or little germs, developed into cells and organs similar to those from which they came. 3. Germinal Continuity and Somatic Dis- continuity. Many ingenious hypotheses have been devised to explain beliefs which are not correct, and this is one of them. The doctrine that adult organisms manufacture germ cells and transmit their characters to them is known to be erroneous. Neither germ cells nor any other kind of cells are formed by the body as a whole, but every cell in the body THE CELLULAR BASIS 93 comes from a preceding cell by a process of di- vision, and germ cells are formed, not by con- tributions from all parts of the body, but by division of preceding cells which are derived ultimately from the fertilized egg (Fig. 22). The hen does not produce the egg, but the egg produces the hen and also other eggs. Indi- vidual traits are not transmitted from the hen to the egg, but they develop out of germinal factors which are carried along from cell to cell, and from generation to generation. There is a continuity of germinal substance, and usually of germinal cells, from one gener- ation to the next. In some animals the germ cells are set apart at a very early stage of de- velopment, sometimes in the early cleavage stages of the egg. In other cases the germ cells are first recognizable at later stages, but in practically every case they arise from germinal or embryonic cells which have not differentiated into somatic tissues. Germinal continuity and somatic discontinuity of suc- cessive generations in sexually produced or- ganisms is not a theory but an established fact. In general, germ cells do not come from dif- 94 HEREDITY AND ENVIRONMENT ferentiated somatic cells, but only from un- differentiated germinal cells, and if in a few doubtful cases differentiated cells mav reverse FIG. 22. DIAGRAM SHOW- ING THE "CELL LINEAGE" OF THE BODY CELLS AND GERM CELLS IN A WORM OR MOL- LUSK. The lineage of the germ cells ("germ track") is shown in black, of ecto- derm in white, and of endo- derm and mesoderm in shaded circles. The whole course of spermatogenesis and oogenesis is shown in the lower right of the figure beginning with the primitive sex cells (Prim. Sex Cells) and ending with the game- tes, the genesis of the sper- matozoa being shown on the left and that of the ova on the right. THE CELLULAR BASIS 95 the process of development and become embry- onic cells and even germ cells it does not destroy this general principle of germinal con- tinuity and somatic discontinuity. Thus the problem which faces the student of heredity and development has been cut in two; he no longer inquires how the body pro- duces the germ cells, for this does not happen, but merely how the latter produce the body and other germ cells. The germ is the unde- veloped organism which forms the bond be- tween successive generations ; the person is the developed organism which arises from the germ under the influence of environmental conditions. The person develops and dies in each generation ; the germ-plasm is the contin- uous stream of living substance which con- nects all generations. The person nourishes and protects the germ, and in this sense the person is merely the carrier of the germ-plasm, the mortal trustee of an immortal substance. This contrast of the germ and the person, of the undeveloped and the developed organ- ism, is fundamental in all modern studies of heredity. It was especially emphasized by 96 HEREDITY AND ENVIRONMENT Weismann in his germ-plasm theory and recently it has been made prominent by Johannsen under the terms "genotype" and "phenotype" ; the genotype is the fundamental hereditary constitution of an organism, it is the germinal type; the phenotype is the de- veloped organism with all of its visible char- acters,, it is the somatic type. But important as this distinction is between germ and soma it has sometimes been over- emphasized. This is one of the chief faults of Weismann's theory. The germ and the soma are generically alike, but specifically different. Both germ cells and somatic cells have come from the same oosperm, but have differentiated in different ways; the tissue cells have lost certain things which the germ cells retain and have developed other things which remain un- developed in the germ cells. But the germ cells do not remain undifferentiated ; both egg and sperm are differentiated, the former for receiving the sperm and for the nourishment of the embryo, the latter for locomotion and for penetration into the egg. But while the differentiations of tissue cells are usually irre- THE CELLULAR BASIS 97 versible, so that they do not again become germinal cells, the differentiations of the sex cells are reversible, so that these cells, after their union, again become germinal cells. In many theories of heredity it is assumed that there is a specific "inheritance material," distinct from the general protoplasm, of which the function is the "transmission" of hereditary properties from generation to generation, and of which the characteristics are independence of the general protoplasm, continuity from generation to generation and extreme stability in organization. This is the idioplasm of Xageli, the germ-plasm of Weismann. But there is no reason to suppose that "germ- plasm" is anything other than germinal proto- plasm, which is found in all cells in the earliest stages of development but which becomes limited in quantity or altered in quality in tissue cells. A "germ-plasm" which is abso- lutely distinct from and independent of the general protoplasm is a mere fiction which finds no justification in reality. 4. The Units of Living Matter. The en- tire cell, nucleus and cytoplasm, is the ulti- 98 HEREDITY AND ENVIRONMENT mate unit of living matter which is capable of independent existence. Neither the nucleus nor the cytoplasm can for long live independ- ently of each other, but the entire cell can perform all the fundamental vital processes. It transforms food into its own living material, it grows and divides, it is capable of respond- ing to many kinds of stimuli. But while the parts of a cell are not capable of independent existence they may perform certain of these vital processes. Not only is the cell as a whole capable of assimilation, growth and division, but every living part of the cell has this power. The nucleus builds foreign substances into its own substance, and after it has grown to a certain size it divides into two ; the cytoplasm does the same, and this process of assimilation, growth and division occurs in many parts of the nu- cleus and cytoplasm, such as the chromosomes, chromomeres, centrosomes, etc. In all cases cells come from cells, nuclei from nuclei, chromosomes from chromosomes, centrosomes from centrosomes, etc. Indeed, the manner in which all living mat- THE CELLULAR BASIS 99 ter grows indicates that every minute particle of protoplasm has this power of taking in food substance and of dividing into two particles when it has grown to maximum size. Pre- sumably this power of assimilation, growth and division is possessed by particles of protoplasm which are invisible with the highest powers of our microscopes, though it is probable that these particles are much larger than the largest molecules known to chemistry. The smallest particle which can be seen with the most powerful microscope in ordinary light is about 250 (i(i (millionths of a millimeter) in diameter. The largest molecules are probably about 10 ftp in diameter. Between these in- visible molecules and the just visible particles of protoplasm there may be other units of or- ganization. These hypothetical particles of protoplasm have been supposed by many authors to be the ultimate units of assimila- tion, growth and division, and in so far as these units are supposed to be different in different species, or with respect to different hereditary characters, they are known as inheritance units. It is assumed in practically all theories of 100 HEREDITY AND ENVIRONMENT heredity that the "inheritance material," or more correctly the germinal protoplasm, is composed of ultra-microscopical units which have the power of individual growth and di- vision and which are capable of undergoing many combinations and dissociations during the course of development, by which combina- tions and dissociations they are transformed into the structures of the adult. Various names have been given to such units by differ- ent authors; they are the "physiological units" of Herbert Spencer, the "gemmules" of Dar- win, the "plastidules" of Elsberg and Haeckel, the "pangenes" of de Vries, the "plasomes" of Wiesner, the "idioblasts" of Hertwig, the "bio- phores" and "determinants" of Weismann. With the publication of Weismann's work on the germ-plasm in 1892 speculation with regard to these ultra-microscopic units of life and of heredity reached a climax and began to decline, owing to the highly speculative character of the evidence as to the existence, nature and activities of such units. But with the rediscovery of Mendel's principles of heredity the necessity of assuming the exist- THE CELLULAR BASIS 101 ence of inheritance units of some kind once more became evident, and, without attempting to define what such units are or how they be- have modern students of heredity invariably accept their existence. They are now called determiners or factors or genes, and are usu- ally thought of as elements or units of the germ cells which condition the characters of the developed organism, and which are in a measure independent of one another; though of course neither they nor any other parts of a cell are really independent in the sense that they can exist apart from one another. They are to be thought of as we think of certain chemical radicals which exist only in combina- tion with other chemical elements in the form of molecules, and yet may preserve their iden- tity in many different combinations. If there are inheritance units, such as de- terminers or genes, as practically all students of heredity maintain, they must be contained in the germ cells, and it becomes one of the fundamental problems of biology to find out where and what these units are. But whether we assume the existence of these units or not 102 HEREDITY AND ENVIRONMENT we know that the germ cells are exceedingly complex, that they contain many visible units such as chromosomes, chromomeres, plasto- somes and microsomes, and that with every great improvement in the microscope and in microscopical technique other structures are made visible which were invisible before, and whether the particular hypothetical units just named are present or not seems to be a matter of no great importance, seeing that, so far as the analysis of the microscope is able to go, there are in all protoplasm differentiated units which are combined into a system; in short, there is organization. 5. Heredity and Development. The germ cells are individual entities and after the ferti- lization of the egg the new individual thus formed remains distinct from every other in- dividual. Furthermore, from its earliest to its latest stage of development it is one and the same organism; the egg is not one being and the embryo another and the adult a third, but the egg of a human being is a human being in the one-celled stage of development, and the characteristics of the adult develop out of the THE CELLULAR BASIS 103 egg and are not in some mysterious way grafted upon it or transmitted to it. Parents do not transmit their characters to their offspring but their germ cells in the course of long development give rise to adult characters similar to those of the parents. The thing which persists more or less completely from generation to generation is the organiza- tion of the germ cells which differentiate in similar ways in successive generations if the ex- trinsic factors of development remain similar. In short, heredity may be defined as the appearance in offspring of characters whose differential causes are found in the germ cells. Heritage is the sum of all those qualities which are determined or caused by this germinal or- ganization. Development is progressive and coordinated differentiation of this germinal or- ganization, by which it is transformed into the adult organization. Differentiation is the for- mation and localization of many different kinds of substances out of the germinal substance, of many different structures and functions out of the relatively simple structures and functions of the oosperm. 104 HEREDITY AND ENVIRONMENT This germinal organization influences not merely adult characters but also the character of every stage from the egg to the adult con- dition. For every inherited character, whether embryonic or adult, there is some germinal basis. We receive from our parents germ cells of a particular kind and constitution, and under given conditions of environment these cells undergo regular transformations and differentiations in the course of development, differentiations which lead to particular adult characteristics. In the last analysis the causes of heredity and development are problems of cell structures and functions, problems of the formation of particular kinds of germ cells, of the fusion of these cells in fertilization, and of the subsequent formation of the various types of somatic cells from the fertilized egg cell. B. THE GERM CELLS Observations and experiments on developed animals and plants have furnished us with a knowledge of the finished ' products of inheri- tance, but the actual stages and causes of in- heritance, the real mechanisms of heredity, are THE CELLULAR BASIS 105 to be found only in a study of the germ cells and of their development. Although many phenomena of inheritance have been dis- covered in the absence of any definite knowl- edge of the mechanism of heredity, a scientific explanation of these phenomena must wait upon the knowledge of their causes. In the absence of such knowledge it has been neces- sary to formulate theories of heredity to ac- count for the facts, but these theories are only temporary scaffolding to bridge the gaps in our knowledge, and if we knew all that could be known about the germ cells and their de- velopment we should have little need of theories. In the first lecture we looked at the germ cells and their development from the outside, as it were ; let us now look inside these cells and study their minuter structures and functions. Only a beginning has been made in this minute study of the germ cells and of their transformation into the developed animal, and it seems probable that it may engage the attention of many future generations of bi- ologists, but nevertheless we have come far FIG. 23 For Description see page 107 THE CELLULAR BASIS 107 since that day, only about thirty-five years ago, when Oscar Hertwig first saw the ap- proach and union of the egg and sperm nuclei within the fertilized egg. Indeed so rapid has been the advance of knowledge in this field that many of the pioneers in this work are still active in research. 1. Fertilization. The development of the individual may be said to begin with the ferti- lization of the egg, though it is evident that both egg and sperm must have had a more re- mote beginning, and that they also have un- dergone a process of development by which their peculiar characteristics of structure and function have arisen; a subject to which we shall return later. But the developmental processes which lead to the formation of fully FIG. 23. DIAGRAMS OF THE MATURATION AND FERTILIZATION OF THE EGG OF A MOLLUSK (Crepidula). A, B. First matura- tion division (1st Mat. Sp.) C. Second maturation division (2d Mat. Sp.) and first polar body (1st PB) resulting from first division. <$N, sperm nucleus, gC, sperm centrosome. D. Approach of sperm nucleus (> 3 & 00 (00 FIG. 51. Diagram of Mendelian inheritance, in which the individual is represented by the large circle, the germ cells by the small ones, dominants being shaded and recessives white, a, Pure dominant X pure recessive = all dominant- recessives, b, Dominant-recessive X dominant-recessive = 1 pure dominant : 2 dominant-recessives : 1 pure recessive, c, Dominant-recessive X pure dominant = 2 pure dominant : 2 dominant = recessive, d, Dominant-recessive X pure reces- sive 2 dominant-recessive : 2 pure recessive. PHENOMENA OF INHERITANCE 237 Other Mendelian Ratios When a pure dominant is crossed with a mixed dominant-recessive all the offspring show the dominant character, though one-half are pure dominants and the other half domi- nant-recessives. Thus if a pure round-seeded variety of pea is crossed with a hybrid between a round- and a wrinkled-seeded one, all the progeny are round-seeded, though one half of them carry the factor for wrinkled seed; this may be graphically represented as follows, R representing the factor for round seed and W that for wrinkled seed: $ germ cells R \ , R ? germ cells R /\ W Possible combinations 2 RR: 2 R (W). In subsequent generations the progeny of the pure round (RR) breed true and produce only round-seeded peas, whereas the progeny of the hybrid round-wrinkled (RW) split up into pure round, hybrid round-wrinkled, and pure wrinkled in the regular Mendelian ratio oflRR:2R(W) : 1 WW (Fig. 52). 238 HEREDITY AND ENVIRONMENT When a pure recessive is crossed with a mixed dominant-recessive another typical ratio results. Thus if a wrinkled-seeded variety of pea is crossed with a hybrid between a round- and wrinkled-seeded one, round-seeded and wrinkled-seeded peas are produced in the pro- portion of 1 : 1. This is due to the fact that the hybrid produces two kinds of germ cells, the pure-bred but one, and the possible combi- nations of these are as follows: ? germ cells W \ / W $ germ cells R ^ W Possible combinations 2 R W: 2 WW . This ratio of 1 : 1 is approximately the ratio of the two sexes in many animals and plants, and there is good reason to believe that sex is a Mendelian character of this sort, in which one parent is heterozygous for sex and the other homozygous (Fig. 51, d). 2. Results of Crossings where there is more than one Pair of Contrasting Characters. It rarely happens that two individuals differ in a single character only; more frequently they differ in many characters, and this leads to a PHENOMENA OF INHERITANCE 239 great increase in the number of types of off- spring in the F 2 generation. t But however many pairs of contrasting characters the par- ents may show each pair may be considered by itself as if it were the only contrasting pair, and when this is done all the offspring may be classified according to the regular Mendelian formula given above. But when two or more contrasting charac- ters of the parents are followed to the F 2 gen- eration many permutations of these characters occur, thus giving rise to a larger number of types of individuals than when a single pair of characters is concerned. When there is only one pair of contrasting characters there are usually but two types of offspring apparent in the F 2 generation, viz., dominants and reces- sives in the ratio of 3:1 (Fig. 52) ; where there are two pairs of contrasting characters in the parents there are four types of offspring in the Fo generation in the ratio of (3 : I) 2 = 9:3:3:1; when there are three pairs of con- trasting characters in the parents there are eight types of offspring apparent in the F 2 generation in the proportions of (3 : I) 3 = 240 HEREDITY AND ENVIRONMENT 27:9:9:9:3:3:3:1, etc. Thus when Mendel crossed a variety of peas bearing round and yellow seeds with another variety having wrinkled and green seeds all the offspring of the Fi generation bore round and yellow seeds, round being dominant to wrinkled, and yellow to green. But the plants raised from these seeds, when self-fertilized, yielded seeds of FIG. 52. Monohybrid Diagram showing results of crossing round (R) seeded with wrinkled (W) seeded peas. Large cir- cles represent zygotes, small ones, or single letters, gametes. In Fj all individuals are round but contain round and wrinkled gametes. In F 2 the g gametes are placed above the square, the $ ones to the left, and the possible combinations of and 5 gametes are shown in the small squares, the relative numbers of different types being 1 RR:2 R(W):1 WW. PHENOMENA OF INHERITANCE 241 four types, round and yellow (RY), wrinkled and yellow (WY), round and green (RG), and wrinkled and green (WG) in the propor- tion of 9 : 3 : 3 : 1 as shown in Fig. 53. In this case also this ratio may be explained YRCGW) 2T7 YR YR YW GR GW YW GR GW F^ FIG. 53. Dihybrid Diagram showing results of crossing peas having yellow-round (YR) seeds with others having green- wrinkled (GR) ones. Four types of germ cells are formed by such a hybrid, viz. YR, YW, GR, GW, and the 16 possible combinations (genotypes) of these $ and $ gametes are shown in the small squares. Since recessive characters do not ap- pear when mated with dominant ones these 16 genotypes pro- duce 4 phenotypes in the following relative numbers: 9YR: 3YW:3GR:1GW. There is 1 pure dominant (upper left cor- ner), 1 pure recessive (lower right corner), 4 homozygotes in diagonal line between these corners, and 12 heterozygotes. 242 HEREDITY AND ENVIRONMENT by assuming that the germ cells (ovules and pollen) are pure with respect to each of the contrasting characters, round-wrinkled, yel- low-green, and therefore any combination of these may occur in a germ cell except the com- binations EW and YG. Accordingly there are four possible kinds of germ cells as follows : Y G V i.e. YH, YW, GR, GW. R / \ W Each of these four kinds of pollen may fertilize any of the four kinds of ovules, thus giving rise to sixteen combinations, no two of which are alike, as shown in Fig. 53. The dominant characters are in this case round and yellow, and only when one of these is absent can its contrasting character, wrinkled or green, develop. Accordingly the sixteen possible combinations yield seeds of four different ap- pearances and in the following proportions: 9RY:3RG:3WY:IWG. Only one individual in each of these four classes is pure (homozy- gous) and continues to breed true in successive generations; in Fig. 53 these are found in the diagonal from the upper left to the lower PHENOMENA OF INHERITANCE 243 right corner. All other individuals are heter- ozygous and show Mendelian splitting in the next generation. When parents differ in three contrasting characters a much larger number of combina- tions is possible in the F 2 generation. Thus if a pea with round (R) and yellow (Y) seeds, and with tall (T) stem is crossed with one having wrinkled (W) and green (G) seeds, and dwarf ( D) stem all the progeny of the FI generation have round and yellow seeds and tall stem, It, Y, and T being dominant to W, G, and D. But in the F 2 generation there are sixty-four possible combinations (genotypes) of these six characters; but since a recessive character does not develop if its contrasting dominant character is present there are only eight types which come to expression (phenotypes) and in the following numbers: 27RYT : 9RYD : 9RGT : 3RGD : 9WYT : 3WYD : 3WGT : 1WGD. Of these sixty- four genotypes only eight are homozygous and breed true (those lying in the diagonal be- tween upper left and lower right corners in Fig. 54), while only one is pure dominant 244 HEREDITY AND ENVIRONMENT and one pure recessive (the ones in the upper left and lower right corners of Fig. 54) . When the parents differ in one character only, the offspring formed by their crossing are called monohybrids, when there are two contrasting characters in the parents the off- spring are dihybrids, when three, trihybrids, and when the parents differ in more than three characters the offspring are called polyhybrids. There are certainly few cases in which parents actually differ in only a single character, but since each contrasting character may be dealt with separately, as if it were the only one, and since the number of types of offspring in- creases greatly when more than one or two characters are considered at the same time, it is customary to deal simultaneously with only one or two characters of hybrids, even though the parents may have differed in many characters. 3. Inheritance Formulae. Mendel repre- sented the hereditary constitution of the plants used in his experiments by letters employed as symbols, dominant characters being repre- sented by capitals and recessives by small let- RYT RYT RYD RGT ROD WYT WYO WGT WGD FIG. 54. Trihybrid Diagram showing results of crossing peas having round-yellow seeds and tall stem (RYT) with peas having wrinkled-green seeds and dwarf stem (WGD). Eight types of germ cells result from such a hybrid, as shown in the <$ gametes above the square and the $ ones to the left of it, and the possible combinations (genotypes) of these and $ gametes are shown in the 64 small squares of which only 1 is pure dominant (upper left corner), 1 pure recessive (lower right corner) and 8 homozygotes (in di- agonal line between these corners). The relative numbers of the different phenotypes are 27RYT: 9RYD: 9RGT: 9 WYT: 3RGD: 3WYD: 3WGT: 1WGD. 246 HEREDITY AND ENVIRONMENT ters. The seven contrasting characters of his peas could be represented as follows: Seeds, round (A), or wrinkled (a) ; yellow (B), or green (b) ; with gray seed coats (C), or white seed coats (c). Pods, green (X)), or yellow (d) ; inflated (E), or constricted (e). Habit, tall (F), or dwarf (/). Flowers, axial (G), or terminal (g). It is possible for one plant to have all of these dominant characters or all of the reces- sive ones, or part of one kind and part of the other. The inheritance formula of a plant having all seven of the dominant characters is ABCDEFG; of one having all of the recessive characters abcdefg. When two such plants are crossed the inheritance formula of the hy- brid is AaBbCcDdEeFfGg, and since the dominant and recessive characters (or rather determiners of characters) represented by these seven pairs of letters separate in the for- mation of the gametes, and since each separate determiner may be associated with either mem- ber of the six other pairs, the number of possi- ble combinations of these determiners in the PHENOMENA OF INHERITANCE 247 gametes is (2) 7 or 128. That is, in this case 128 kinds of germ cells may be produced, each having a different inheritance formula; and since each of these 128 kinds of male germ cells may unite with any one of the 128 kinds of female germ cells, the number of possible combinations is (128) 2 or 16,384, which repre- sents the number of combinations of these char- acters which are possible in the F 2 generation. Every one of these more than sixteen thousand genotypes may be represented by various com- binations of the letters ABCDEFG and abcdefg. When many characters are concerned it is difficult to remember what each letter stands for, and consequently it is customary in such cases to designate characters by the initial let- ter in the name of that character. By this form of short hand one can show in a graphic way the possible segregations and combina- tions of hereditary units in gametes and zy- gotes through successive generations, and as a result many modern works on Mendelian inheritance look like pages of algebraic formulae. 248 HEREDITY AND ENVIRONMENT Some progress has been made, as was pointed out in the last lecture, in identifying certain structures of the germ cells with cer- tain hereditary units, but quite irrespective of what these units may be and where they may be located it is possible, by means of the Men- delian theory of segregation of units in the germ cells and of chance combinations of these in fertilization to predict the number of geno- types and phenotypes which may be expected as the result of a given cross. 4. Presence and Absence Hypothesis. Mendel spoke of the presence of contrasting or differentiating characters in the plants which he crossed, such as round or wrinkled seeds, tall or short stems, etc. Many other writers regard these contrasting characters as positive and negative expression of a single character, and consequently they speak of the presence or absence of single characters: thus round seeds are due to the presence of a factor for roundness (A) while wrinkled seeds are characterized by the absence of that factor (a). Round seeds are wrinkled seeds plus the factor for roundness. Most of the phenomena PHENOMENA OF INHERITANCE 249 of Mendelian inheritance are more simply stated in terms of presence or absence of single characters than in terms of contrasting characters. When both gametes carry similar positive factors the zygote has a "double dose" of such factors and is said to be duplex; when only one of the gametes carries such a factor the zygote has a "single dose" and is simplex, when neither gamete carries a positive factor or fac- tors, the zygote receives only negative factors and is said to be nulliplex. Thus the union of gametes AB (?) and AB ( "^ ^ FIG. 61. Diagram of inheritance of color blindness through the male. A color blind male (here black) transmits his defect to his grandsons only. The corresponding distribution of the sex chromosomes is shown on the right, the one carry- ing the factor for color blindness being black. (After Morgan.) PHENOMENA OF INHERITANCE 277 normal mother have only normal children, but the father transmits to his daughters and not to his sons the sex-determiner which carries the factor for color blindness. But since color blindness does not develop in fe- males unless it is duplex (i.e. comes from both father and mother) whereas it develops in males if it is simplex (i.e. comes from either parent) all the daughters of a color blind Chromosomes W/ffo VV &y A A Parents c? ? *, ' Gametes Fi Gametes <0>e- tweenjthesejtwajextremes.. Our personalities were not absolutely predetermined in the germ cells from which we came, and yet they have arisen from those germ cells and have been conditioned by them. When it is said that any characteristic is predetermined in the germ cell, what does this mean? What but that the development of that characteristic is made pos- sible? Adult characteristics are potential and not actual in the germ, and their actual ap- pearance depends upon many complicated re- actions of the germinal units with one another and with the environment. In short, our ac- tual personalities are not predetermined in the germ cells, but our possible personalities are. 2. The Determinism of Environment. This determinism of heredity is matched by a corresponding determinism of environment. Life is possible only within rather narrow limits of physical and chemical conditions and in the main these limits are fixed by the con- stitution of nature. But apart from these an- tecedent conditions of life in general there are many minor conditions of environment which 454 HEREDITY AND ENVIRONMENT exercise a profound influence upon organisms, especially in the course of their development. Very slight changes in food, temperature, moisture and atmospheric conditions may pro- duce great changes in the developing organ- ism, and these conditions are for the most part entirely beyond the control of the indi- vidual affected. In all organisms the potentialities of de- velopment are much greater than the actuali- ties. In many animals a small part of the body is capable, when separated from the re- mainder, of producing a whole body, though this potency would never have become an ac- tuality except under the stimulus of separa- tion. In like manner a part of an egg may, when separated from the remainder, give rise to an entire animal. By modifying the con- ditions of development animals may be pro- duced which have one eye, many eyes or no eyes; animals in which the body is turned in- side out, or side for side; animals in which all sorts of dislocation of organs have taken place ; and the earlier the environmental forces act the more profound are the modifications. GENETICS AND ETHICS 455 But leaving out of account all forms which are so monstrous that they are incapable of reaching maturity we find that there are left many variations in the size and vigor of the body as a whole, as well as of its parts ; many variations in the more or less perfect correla- tion of these parts with one another, which were determined by the conditions of develop- ment rather than by heredity. In a given germ cell there is the potency of any kind of organ- ism that could develop from that cell under any kind of conditions. The potencies of de- velopment are much greater than the actuali- ties. Anything which could possibly appear in the course of development is potential in heredity and under given conditions of en- vironment is predetermined. Since the en- vironment cannot be all things at once many hereditary possibilities must remain latent or undeveloped. Consequently the results of de- velopment are not determined by heredity alone but also by extrinsic causes. Things cannot be predetermined in heredity which are not also predetermined in environment. Of all animals I suppose that man enjoys 456 HEREDITY AND ENVIRONMENT the most extensive and the most varied en- vironment, and its effect upon his personality is correspondingly great. Of all animals man has the longest period of immaturity and it is during this period that the play of environ- mental stimuli on the organism is effective in modifying development. In addition to the material environment he lives in the midst of intellectual, social and moral stimuli which are potent factors in his development. By means of his power to look before and after he lives in the future and past as well as in the pres- ent; through tradition and history he becomes an heir of all the ages. The modifying influ- ences of all these environmental conditions on personality are very great. Each of us may say with Ulysses: "I am a part of all that I have met." So great is the power of environ- ment on the development of personality that it may outweigh inheritance ; a relatively poor in- heritance with excellent environmental condi- tions often produces better results than a good inheritance with poor conditions. Of course no sort of environment can do more than bring out the hereditary possibilities, but on the GENETICS AND ETHICS 457 other hand those possibilities must remain latent and undeveloped unless they are stimu- lated into activity by the environment. Functional activity or use is one of the most important factors of development. Func- tional activity is response to stimuli, which may be external or internal in origin. The entire process of development may be regarded as an almost endless series of such responses on the part of the organism, whether germ cell, embryo or adult, to external and internal stimuli. It is a truism that use strengthens a part and disuse weakens it; it is likewise a truism that responses which are oft repeated become more rapid and more perfect, and in this way habits are formed. Practically all education, whether of man or of lower ani- mals, consists in habit formation, in establish- ing constant relations between certain external or internal stimuli and certain responses of the organism. At first these stimuli are largely of external origin ; later the external stimuli may be replaced more and more by internal ones; but whatever the source of the stimulus the response of the organism to these stimuli is 458 HEREDITY AND ENVIRONMENT one of the most important factors of develop- ment, whether of the body or of the mind. The influence of environment upon the minds and morals of men is especially great. To a large extent our habits, words, thoughts ; our aspirations, ideals, satisfactions; our re- sponsibility, morality, religion are the results of the environment and education of our early years. It cannot be doubted that if we had been born in other countries or ages we should have been different from our present selves in many important respects ; if we had been born and reared in the slums of great cities we should have been other than we are; indeed if the little illnesses, accidents and contingencies of our lives had been different we should have been different in our bodies and minds, as iden- tical twins come to differ from each other under such circumstances. The conditions of early life and education have a great influence in shaping personality and are almost as much beyond the control of the individual as is heredity. If personality in all of its main features is fixed by heredity and environment over which GENETICS AND ETHICS 459 the individual has little or no qontrol, and this is certainly true, personality is as inevitably de- termined by its antecedents as is any other natural phenomenon. This is, I believe, a conclusion from which there is no escape. How then is it possible to believe in freedom and responsibility? Is there not justification for the view so often expressed of late that man is never free and that responsibility and duty are mere delusions? III. DETERMINISM AND RESPONSIBILITY Many persons who have thought upon these subjects have felt, apparently, that there was no tenable middle ground between extreme voluntarism and extreme mechanism ; man has been regarded as a "free agent" or a mere "automaton," absolutely free or absolutely bound, wholly indeterminate or wholly prede- termined. But these extreme views are unreal, unscientific and unjustifiable, for they contra- dict the facts of experience. We have the as- surance of experience that we are not abso- lutely free nor absolutely bound, but that we 460 HEREDITY AND ENVIRONMENT are partly free and partly bound; the alterna- tives are not merely, freedom or determinism, but rather freedom and determinism. 1. Determinism not Fatalism. Whatever the philosophical meaning of "determinism" may be, all that is meant by that term in science and in actual life is that every effect is the re- sultant of antecedent causes and that identical causes yield identical results. Determinism does not mean predeterminism : the one finds every effect to be due to a long chain of pre- ceding causes, the other attributes every effect to a single original cause; the one is scientific naturalism, the other is fatalism. Applying .this to personality actual experi- ence teaches that constant conditions of he- redity and environment give constant results in development and that different conditions give different results. Undoubtedly the entire personality, body and mind, undergoes de- velopment, and modifications of either heredity or environment modify personality. This is scientific determinism, but it is not fatalism and it is not incompatible with a certain amount of freedom and responsibility. GENETICS AND ETHICS 461 2. Control of Phenomena and of Self. Even the most extreme mechanists, who main- tain that we are mere automata and that we could never do otherwise than we do, admit the possibility of a certain amount of control over phenomena outside ourselves. They tell us that the aim of science is not merely to under- stand but also to control nature. But if man may to a limited extent control physical, chem- ical and biological processes in the world around him, if he may control to a limited ex- tent the behavior of a star-fish or dog or child, on what ground is it possible to deny a similar control of his own behavior? Does it not come to this that all such control means intelligent action, or rather the introduction of intelli- gence as a factor in the chain of cause and effect? Before the appearance of intelligence, whether in ontogeny or in phylogeny, no such control of phenomena or of self is possible, but when intelligence becomes a factor in be- havior a limited control of the world and of the self is made possible. Of course man has no control over events which have already happened. Our heredity and early development are accomplished facts 462 HEREDITY AND ENVIRONMENT which nothing can change. Development is not a reversible process; a man cannot enter a second time into his mother's womb and be born again. Once the sex cells are formed their hereditary nature is determined ; once the egg is fertilized the hereditary possibilities of the new individual are fixed ; once any stage of development has passed that page in the book of life is closed and sealed. And yet at every step in this long process of development there were one or more alterna- tives which might have been taken instead of the one which was taken. There were innu : merable possible alternatives in the matings of our ancestors, there were billions of possible alternatives in the union of the millions of types of germ cells which each of our parents produced ; at every step in the development of the oosperm from which each of us came there were many possible alternative stimuli and re- sponses. But in each case one of these in- numerable alternatives was taken and the oth- ers left. In every instance there was some cause that determined which alternative was taken, but these causes are so local and indi- GENETICS AND ETHICS 463 vidual that they cannot be generalized; one cause works in one instance, another in an- other, and so we say that chance determines which alternative is taken, meaning by chance only this that the causes involved cannot be generalized. At critical stages in this process of development the alternatives are so evenly balanced that minor considerations, which we call chance, determine which path shall be taken; but there are no backward steps in de- velopment and once a path has been taken that particular crisis or turning point does not occur again. Thus each of us has wandered through the maze of life, chance usually determining which path shall be taken of the many which heredity and environment offer, until he has come to a stage where associative memory makes it pos- sible to profit by experience and where intel- lect and will make possible intelligent choice. With the growth of intellect and will there comes to be a limited degree of freedom and responsibility, and with increasing complexity of organization the number of alternative paths is greatly increased. The possible reac- 464 HEREDITY AND ENVIRONMENT tions of germ cells are relatively few and fixed, the possible reactions of a complex ani- mal are relatively many and behavior is more plastic; and thus this very complexity and plasticity allow adaptations to the minutest al- terations of environment. 3. Birth and Growth of Freedom. In ani- mals below man and in the stages of human development one may trace the birth and growth of freedom. Even in some of the simplest organisms one can observe inhibitions of responses and modifications of behavior which seem to be due to conflicting stimuli or to changes in the physiological state. In higher organisms such inhibitions or modifica- tions proceed particularly from internal stimuli, which in turn are. probably conditioned by hereditary constitution and past experience. The factors which determine behavior are not merely the present stimulus and the heredi- tary constitution, but also the experiences through which the organism has passed and the habits which it has formed. A moth cannot avoid the impulse to fly toward the light, and it does not learn by ex- GENETICS AND ETHICS 465 perience to avoid the flame. Its reactions are relatively fixed and machine-like. Many other animals learn by experience to inhibit respon- ses to certain stimuli; a tame fish or frog will take food from your hand, but if it is repeat- edly frightened when it attempts to take food it will not come near you though it is starv- ing, it inhibits the strong impulse of a hungry animal to take food by the counter impulse of unpleasant memories or of fear. Here we have the beginnings of what we call freedom, the immediate response to a stimulus is suppressed, internal stimuli are balanced against external ones and final action is de- termined largely by past experience. Owing to his vastly greater power of memory, reflec- tion and inhibition man is much freer than any other animal. Animals which learn little from experience have little freedom and the more they learn the freer they become. In both ontogeny and phylogeny there has been development of freedom. The reactions of germ cells and of the lowest organisms are relatively fixed. In more complex organisms reactions become modifiable through conflict- 466 HEREDITY AND ENVIRONMENT ing stimuli, intelligence, inhibitions. Freedom is the more or less limited capacity of the high- est organisms to inhibit instinctive and non- rational acts by intellectual and rational stimuli and to regulate behavior in the light of past experience. Such freedom is not un- caused activity, but freedom from the mechan- ical responses to external or instinctive stimuli, through the intervention of internal stimuli due to experience and intelligence. To the person accustomed to think of will and choice as absolutely free this may seem to be a sort of freedom so limited as to be scarcely worth the having; and yet "it is the dawning grace of a new dispensation," the beginnings of rational life, social obligations, moral responsibility. The only control over natural phenomena which is possible is in choosing between alter- natives which are offered ; and the only control which one who has reached the age of intelli- gence can have over his own development con- sists in choosing between the alternatives which are open to him. He may not choose his he- redity or early development for the alternative paths which were once offered here have long GENETICS AND ETHICS 467 since been passed; but to a limited extent he may choose his present environment and train- ing, he may choose a path which leads to dis- cipline and increased powers of self-control or the reverse, and to this extent only is he respon- sible for what he may become. 4. Responsibility and Will. All organisms are capable of responding to chemical and physical stimuli but in addition normal men have the capacity of responding to stimuli of a higher order. By responsibility in this higher sense I understand the ability on the part of the organism to respond to rational, social and ethical stimuli or impulses and to inhibit responses to stimuli of an opposite na- ture, and the corresponding expectation on the part of others that the individual will so respond. The psychical stimuli which influ- ence our behavior are not merely remembered experiences but the words, suggestions, ad- monitions, ideas which come to us from others, as well as the almost endless permutations of such memories and suggestions in our thoughts. The social and ethical stimuli are not merely such as arise from love of reward 468 HEREDITY AND ENVIRONMENT and fear of punishment or the desire for praise and the fear of blame but also from the deep seated social instinct to do good, which may reach the highest levels of altruism and self sacrifice. The higher the type of organization the larger is the range of stimuli to which it will respond and the larger the number and kind of responses which may be called forth; and at the same time the larger becomes the power of inhibition of responses whether through the balancing of one stimulus against another or from whatever cause. Human responsibility varies with the complexity of the stimuli in- volved- as well as with the capacity of indi- viduals to respond to those stimuli. A man might be quite responsible in savage society who would be quite irresponsible in civilized communities. In an infant there is no capacity to respond to rational, social or ethical stimuli but with increasing capacity in this respect comes increasing responsibility. Mental and ethical imbeciles, insane and mentally defective persons have a low capacity for such responses and inhibitions and consequently less is ex- GENETICS AND ETHICS 469 pected of them. There are in different men all degrees of responsibility, as there are all degrees of capacity. In one and the same in- dividual responsibility varies at different times and under different circumstances ; it rises and falls, like the tides, in every life. Varying ca- pacity to respond to rational, social and ethical stimuli and to inhibit responses of an opposite nature depends not merely upon inheritance but also upon training, habits, physiological states. The common opinion that all normal men are equally responsible is not correct; in the eyes of the law this may be true, because legal obligations are so far below the capacities of normal men that all may be held equally re- sponsible before the law, though in reality their responsibilities are as varied as their in- heritance or their training. Conversely the responsibility of society to the individual is universally recognized. Ir- responsible persons must be cared for by older or wiser persons who become responsible for them; and in general the responsibility rests upon society to provide as favorable environ- ment as possible for all its members. Ex- 470 HEREDITY AND ENVIRONMENT perienced persons can to a certain extent choose their own environment and thus indi- rectly control their responses and habits but young children are almost if not quite as in- capable of choosing their environment as of choosing their heredity, and it becomes the duty of society to see to it that the environ- mental stimuli are such as to develop rational, social and ethical habits rather than the reverse. We need not think of the will as a deus ex machina, nor even as "a little deity encapsuled in the brain," but rather as the sum of all those psychical processes, such as memory and rea- son, which regulate behavior. In this sense the will is as free as the mind, and no freer. In- deed the will is the mind acting as internal stimulus, inhibition, regulation; in this sense the existence and power of will is no more to be doubted than the existence of those other mental conditions which we call intellect or memory. vjust as intellect or memory may be trained to accomplish results which would have been impossible to the untrained mind, so will may GENETICS AND ETHICS 471 be trained to initiate, inhibit or regulate be- havior in a manner quite impossible to one who has not had this training. It is one of the most serious indictments against modern systems of education that they devote so much attention to training memory and intellect and so little attention to the training of will, upon the proper development of which so much depends. 5. Our Unused Talents. Will is indeed the supreme human faculty, the whole mind in action, the internal stimulus which may call forth all the capacities and powers. And yet the will does not directly create nor even dis- cover these powers; they are produced by the factors of development, by heredity, environ- ment and training; and they are usually dis- covered by accident or under the stress of necessity. How often have we surprised our- selves by doing some unusual or prodigious task! What we have once done we feel that we can do again. We realize more or less clearly, depending upon our experience, that what we habitually do is far less than we could do. It is this reserve, upon which we can 472 HEREDITY AND ENVIRONMENT draw on special occasions, that gives us the sense of freedom. In his inspiring address on "The Energies of Men" William James showed that we have reservoirs of power which we rarely tap, great energies upon which we seldom draw, and that we habitually live upon a level which is far below that which we might occupy. Darwin held the opinion, as the result of a lifetime of observation, that men differ less in capacity than in zeal and determination to utilize the powers which they have. In playful comment on the variety and extent of his own life work he said in modest and homely phrase, "It's dogged as does it." It may be objected that the zeal and determination were inherited, but here also the hereditary possibilities become actualities only as the result of use, training, the formation of habits. It is generally admitted that no constant distinction can be recognized between the brain of a philosopher and that of many a peasant. Neither size nor weight of brain nor complexity of convolutions bears any constant relation to ignorance or intelligence, though GENETICS AND ETHICS 473 doubtless an "unlimited microscopist" could find differences between the trained and the untrained brain. The brains of Beethoven, Gauss and Cuvier, although unusually large, have been matched in size and visible complex- ity by the brains of unknown and unlearned persons persons who were richly endowed by nature but who had never learned to use their talents. In all men the capacity for intellec- tual development is probably much greater than the actuality. The parable of the talents expresses a profound biological truth, men differ in hereditary endowments, one receives ten talents and another receives but one; but the used talent increases many fold, the un- used remains unchanged and undeveloped. Happy is he who is compelled to use his tal- ents; thrice happy he who has learned how to compel himself! We shall not live to see the day when human inheritance is greatly im- proved, though that time will doubtless come, but in the meantime we may console ourselves by the thought that we have many half -used talents, many latent capacities, and although we may not be able to add to our inheritance 474 HEREDITY AND ENVIRONMENT new territory we may greatly improve that which we have. Jennings has pointed out as one of the great tragedies of life the almost infinite slaughter of potential personalities in the form of germ cells which never develop. A more dreadful though less universal tragedy is the loss of real personalities who have all the native en- dowments of genius and leadership but who for lack of proper environmental stimuli have remained undeveloped and unknown; the "mute, inglorious Miltons" of the world; the Cassars, Napoleons, Washingtons who might have been; the Newtons, Darwins, Pasteurs who were ready formed by nature but who never discovered themselves. One shudders to think how narrowly Newton escaped being an unknown farmer, or Faraday an obscure bookbinder, or Pasteur a provincial tanner. In the history of the world there must have been many men of equal native endowments who missed the slender chance which came to these. We form the habit of thinking of great men as having appeared only at long intervals, and yet we know that great crises al- GENETICS AND ETHICS 475 ways discover great men. What does this mean but that the men are ready formed and that it requires only this extra stimulus to call them forth? To most of us heredity has been kind kinder than we. know. The possibilities within us are great but they rarely come to full epiphany. What is needed in education more than any- thing else is some means or system which will train the powers of self discovery and self control. Easy lives and so-called "good en- vironment" will not arouse the dormant powers. It usually takes the stress and strain of hard necessity to make us acquainted with our hidden selves, to rouse the sleeping giant within us. How often is it said that the worthless sons of worthy parents are mys- teries; with the best of heredity and environ- ment they amount to nothing, whereas the sons of poor and ignorant farmers, blacksmiths, tanners and backwoodsmen, with few oppor- tunities and with many hardships and disad- vantages, become world figures. Probably the inheritance in these last named cases was no better than in the former, but the environment 476 HEREDITY AND ENVIRONMENT was better. "Good environment" usually means easy, pleasant, refined surroundings, "all the opportunities that money can buy," but little responsibility and none of that self discipline which reveals the hidden powers and which alone should be counted good environ- ment. Many schools and colleges are making the same mistake as the fond parents; luxury, soft living, irresponsibility are not only al- lowed, but are encouraged and endowed and by such means it is hoped to bring out that in men which can only be born in travail. The chief educational value of athletics is found in this that it teaches self control. But in great athletic contests the self control of the spectators is usually inversely proportional to that of the players, and while excess of stimuli } may lead to wholesome and beneficial reactions i in the players it frequently leads to excess of stimulants and to other injurious reactions in the spectators. But college athletics has this much at least in its favor, it trains men who take part in the contests to do their best, to subordinate pleasure, appetite, the desire for a good time, to one controlling purpose ; it I GENETICS AND ETHICS 477 trains them to attempt what may often seem to them impossible, to crash into the hue though it may seem a stone wall, to get out of their bodies every ounce of strength and endurance which they possess. Such training makes men acquainted with their powers and teaches courage, confidence and responsibility. If only we could make young persons ac- quainted in some similar way with their hidden mental and moral powers what a race of men and women might we not have without wait- ing for that uncertain day when the inheri- tance of the race will be improved ! Whatever the stimulus required, whether pride or shame, fear or favor, ambition or loyalty, responsi- bility or necessity, education should utilize each and all of these to teach men self knowl- edge and self control. But it will be said that self control depends upon inheritance, that strong wills and weak wills are such because of heredity. It is true that one man may be born with a potentiality for self control which another man lacks, but in all men this potentiality becomes actuality only through development, one of the princi- 478 HEREDITY AND ENVIRONMENT pal factors of which is use or functional ac- tivity. An amazing number of persons have but little self control. Is this always due to defective inheritance, or is it not frequently the result of bad habits, of arrested develop- ment? To charge defects at once to heredity removes them from any possible control, helps to make men irresponsible, excuses them for making the least of their endowments. To hold that everything has been predetermined, that nothing is self determined, that all our traits and acts are fixed beyond the possibility of change is an enervating philosophy and is not good science, for it does not accord with the evidence. It is amazing that men whose daily lives contradict this paralyzing philoso- phy still hold it, as it were in some water- tight compartment of the brain, while in all the other parts of their being their acts pro- claim that they believe in their powers of self control: they set themselves hard tasks, they overcome great difficulties, they work until it hurts, until they can say with Johannes Miil- ler, Es Tdebt Blut an der Arbeit, and yet in the philosophical compartment of their minds GENETICS AND ETHICS 479 they can say that it was all predetermined in heredity and from the foundations of the world. Whether all the phenomena of life and of mind can be explained on the basis of a purely mechanistic hypothesis or not, that hypothesis must square with the facts and not the facts with the hypothesis. It has always been true of those who "sat apart and reasoned high of fate, free will, foreknowledge absolute" that they have "found no end in wandering mazes lost." Whatever the way out of these mazes may be, whether it. be found in the varied re- sponses of an organism to the same stimulus, to the introduction of memory, intelligence and reason as internal stimuli, or to some form of idealism which finds necessity not in nature but in the spectator, and freedom not in the spectator but in the agent, it is true for those who do not "sit apart and reason high," but who deal merely with evident phenomena, that the way out of these mazes is not to be found in denying the reality of inhibition, atten- tion and control. Because we can find no place in our philosophy and logic for self de~ 480 HEREDITY AND ENVIRONMENT ! termination shall we cease to be scientists and close our eyes to the evidence? The first duty of science is to appeal to fact and to settle later with logic and philosophy. Is it not a fact that the possibilities of our inheritance depend for their realization upon development, one of the most important factors of which is use, functional activity in response to stimuli? Is it not a fact that in many animals behavior is modifiable and that impulses may be in- hibited and controlled? Is it not a fact that experience, intelligence, will are factors in human behavior and that by means of these men are often able to choose between alterna- tives and so to control their own activities as well as external phenomena? Is it not a fact that our capacities are very much greater than our habitual demands upon them? Is it not a fact that belief in our responsibility ener- gizes our lives and gives vigor to our mental and moral fiber? Is it not a fact that shifting all responsibility from men to their heredity or to that part of their environment which is beyond their control helps to make them irresponsible ? GENETICS AND ETHICS 481 This debilitating philosophy in which every- thing is predetermined, in which there is no possibility of change or control, in which there is hypertrophy of intellect and atrophy of will is a symptom of senility whether in men or nations. We need to return to the joys of a childhood age in which men believed them- selves free to do, to think, to strive, in which life was full of high endeavor and the world was crowded with great emprise. We need to think of the possibilities of development as well as of the limitations of heredity. Chance, heredity, environment have settled many things for us ; we are hedged about by bounds which we cannot pass, but those bounds are not so narrow as we are sometimes taught and within them we have a considerable degree of freedom and responsibility. "That which we are we are, One equal temper of heroic hearts Made weak by time and fate, but strong in will To strive, to seek, to find, and not to yield." 482 HEREDITY AND ENVIRONMENT IV. THE INDIVIDUAL, AND THE RACE There is a larger freedom and a greater responsibility than that which characterizes the individual. What the individual cannot do because of weakness, ignorance, self interest, short life, society can accomplish with the strength, wisdom, and interest of all, and through long ages of time. There are many grades of organization from the bacterium to the vertebrate, from the germ cell to the man. Society is the last and highest grade of organi- zation and its freedom and responsibility are to those of the individual very much as the free- dom and responsibility of the developed man are to those of the germ cell from which he came. Out of the correlations, differentiations and integrations of persons has grown this higher type of organization which we call society. 1. The Conflict between the Freedom of the Individual and the Good of Society. The freedom, power and responsibility of society are founded upon limitations of individual free- GENETICS AND ETHICS 483 dom for the good of the race. Among social animals, such as ants and bees, there is so much instinct and so little reason and freedom that there is practically no conflict between the individual and the race, but with the in- crease of intelligence and freedom among men there has developed an increasing conflict be- tween the individual and society. So far as social limitations are artificial, selfish, for the good of a few rather than of all, this conflict of the ages, this struggle to be free has been the crowning glory of mankind. The struggle for freedom from tyranny in thought and speech, in religion, government and industry, no less than for the freedom that comes by the conquest of nature, is one of the greatest achievements of the human race. But social restrictions on individual freedom are not all artificial and selfish. Some of them are absolutely essential not only to the welfare but even to the continued existence of the race* and when demands for individual freedom go to the extent of fighting against these racial obligations they become a serious menace to mankind. 484 HEREDITY AND ENVIRONMENT 2. Perpetuation and Improvement of the Race the highest Ethical Obligation. Among all organisms the race or species is of para- mount importance. Race preservation, not self preservation, is the first law of nature. Among all organisms the perpetuation and welfare of the race are cared for by the strong- est instincts. In very many species of animals reproduction means the death of the individual. The breeding instinct drives every male bee, every male and female salmon, to its certain death in order that the race may be perpetu- ated. Among the higher organisms the strongest of all the instincts are those con- nected with reproduction. But in the human species intellect and freedom come in to inter- fere with instinct. The reproductive instincts are not merely controlled by reason, as they should be, but to an alarming extent they are thwarted and perverted among intelligent people. The struggle to be free is part of a great evolutionary movement, but the freedom must be a sane one which neither injures others nor eliminates posterity. The feminist movement GENETICS AND ETHICS 485 in so far as it demands greater intellectual and political freedom for women may be a benefit to the race but in so far as it demands freedom from marriage and reproduction it is suicidal. The cry of Rachel, "Give me children or I die," has been turned by many modern women to, "I'd rather die than have children." If the demand for individual freedom blinds men and women to their racial obligations the in- evitable decadence and extinction of their lines must follow. In every age and country where demands for personal freedom have been most insistent and extreme, where men and espe- cially women have demanded freedom from the burdens of bearing and rearing children as well as from other natural social obligations, the end has been degeneration and extinction. This has been the history of many talented races and families of mankind. The decay of the most gifted races of the ancient world, especially those of Greece and Rome, was not due primarily to bad heredity nor to bad ma- terial environment but rather to the growth of luxury and selfishness and unrestricted free- dom; marriage became unfashionable, immo- 486 HEREDITY AND ENVIRONMENT rality was widespread, and then came sterility and extinction or mixture with inferior stock and degeneracy. And then the barbarian, the immigrant, the natural man, unspoiled by too much freedom and true to his instincts, came in to take the place of the more gifted race. Truly "there is a power not ourselves that makes for righteousness." In these days when we talk of our race and our civilization as if they were necessarily su- preme and immortal it is well to remember that there have been other races and other civilizations that regarded themselves in the same way. "Assyria, Greece, Rome, Carth- age, where are they?" And what assurance have we that our race and our civilization will not run a similar course and come to a similar end? May we not surely predict that if we continue to put individual freedom and luxury and selfishness above social obligations our race and civilization will also see the writing on the wall, "Thou are weighed in the bal- ances and art found wanting"? In these days when individuals are demanding more and more freedom it is well to remember that "the GENETICS AND ETHICS 487 best use that man has made of his freedom has been to place limitations upon it." Again and again, age after age, men and families and nations have gone up to a climax of greatness and then have declined, while other unknown men have taken their places. Greatness has not for long perpetuated itself. An epitome of human history is contained in the words, "He hath put down the mighty from their seats and hath exalted them of low degree." It may well be asked by those who are in- terested in breeding a better race of men whether such a thing is possible, whether the better race may not be lacking in vitality or fertility or morality and thus be doomed to an early end. Although this has been the fate of many gifted races of the past I do not think that it was a necessary fate. The history of domesticated animals and of cultivated plants, and especially the recent notable advances in genetics, indicate what eugenics might do for the human race. In time, under intelligent guidance, the worst qualities of the race might be weeded out and the best qualities preserved. This is the goal toward which intelligent effort should be directed. This should be the su- 488 HEREDITY AND ENVIRONMENT preme duty of society and of all who love their fellow men. But I think that notable human improve- ment can take place only upon two conditions : (1) The physical and intellectual improve- ment of the individual through environment and training must not interfere with his racial and ethical obligations. Individual freedom must be subordinated to racial welfare. (2) The promotion of human evolution must be undertaken by society as its greatest work. Not only has society greater freedom and greater power than the individual but it per- sists while men come and go. Our hereditary lines are so interwoven with those of other races and will be so entangled with other lines in the future that any selfish or narrow policy of improving our family or class can have little permanent value. We shall rise only as the race rises. Indeed when we con- sider all the influences of our fellow men upon our development, when we consider our he- reditary connections with multitudes of men and women of the past, when we think of the nexus of hereditary strands which are woven GENETICS AND ETHICS 489 into our personalities and which will be con- tinued through us to many future generations, we realize that after all the individual is not really a separate and independent being, but a minor unit in the great organism of hu- manity, and that his greatest duty is to trans- mit unimpaired and undefiled a noble heritage to generations yet unborn. It is possible greatly to improve environ- ment. Conditions of life are still hard and cruel for many. A vast amount of good hu- man material is wasted in modern society. As civilization becomes more complex the quan- tity of human wreckage and garbage ever grows greater. Many useful lives and some great possibilities are blotted out by unfavor- able environment. It is the duty of society as far as possible to conserve these lives and to develop these possibilities. It is possible greatly to improve education, to make it a potent factor in development in- stead of a conventional veneer. In spite of innumerable educational reforms the essential reform has not yet been reached; mere refine- ments of bad methods are not real reforms. 490 HEREDITY AND ENVIRONMENT The essence of all education is self discovery and self control. When education helps an individual to discover his own powers and limi- tations and shows him how to get out of his heredity its largest and best possibilities it will fulfil its real function; when children are taught not merely to know things but particu- larly to know themselves, not merely how to do things but especially how to compel them- selves to do things, they may be said to be really educated. For this sort of education there is demanded rigorous discipline of the powers of observation, of the reason, and es- pecially of the will. It is possible greatly to improve heredity: (a) By weeding out from the possibility of reproduction human stocks bearing serious defects. (b) By cultivating pride in good heredity and by discouraging voluntary in- fertility on the part of those who have a goodly heritage, (c) By increasing opportunities for early and favorable marriages, (d) By care- fully conserving the best human mutations or inherited variations. In this way if in any way the better race will be produced. The GENETICS AND ETHICS 491 possible improvements of heredity are great, the possible improvements of environment and training are great, but whether men of the fu- ture will be better than those of the past or present is a question not only of genetics but also of ethics. How better can I close this course of lec- tures than with the words of Francis Galton, one of the greatest students of human he- redity and the founder of the science of Eu- genics ? "The chief result of these inquiries has been to elicit the religious significance of the doctrine of evolution. It suggests an alteration in our mental attitude and imposes a new moral duty. The new mental attitude is one of a greater sense of moral freedom, responsibility and opportunity; the new duty which is supposed to be exercised concurrently with, and not in opposition to the old ones upon which the social fabric depends, is an endeavor to further evolution, especially that of the human race." REFERENCES TO LITERATURE The following list of books and publications in- cludes only those works which are referred to most frequently in the preceding pages. Several of the books cited, particularly those by Plate and Morgan, contain extensive bibliographies. Those desiring to become more fully acquainted with books and articles dealing with the subjects of heredity and develop- ment are referred to the larger works which are listed here. Books and Larger Works Bateson, W. Materials for the Study of Variation, London, 1894. Bateson, W. Problems in Genetics. Yale Univ. Press. 1913. Bateson, W. Mendel's Principles of Heredity. 3rd Impression, Cambridge, 1913. Baur, E. Einfiihrung in die experimented Verer- bungslehre. Berlin, 1911. Castle, W. Heredity in Relation to Evolution and Animal Breeding. New York, 1912. Castle, W. E.; Coulter, J. M. ; Davenport, C. B. ; East, E. M.; Tower, W. L. Heredity and Eu- genics. Chicago, 1912. Correns, C. Die Neuen Vererbungsgesetze. Berlin, 1912. Darbishire, A. R. Breeding and Mendelian Discov- ery. London, 1911. 493 494 HEREDITY AND ENVIRONMENT Darwin, C. Animals and Plants under Domestica- tion. New York, 1887. Davenport, C. B. Heredity in Relation to Eugen- ics. New York, 1911. De Vries, H. Intracellular Pangenesis. Chicago, 1910. De Vries, H. Die Mutationstheorie. Leipzig, 1901. De Vries, H. Plant Breeding. Chicago, 1907. Doncaster, L. Heredity in the Light of Recent Re- search. Cambridge, 1911. Driesch, H. The Science and Philosophy of the Or- ganism. Gifford Lectures, London, 1908. Ellis, H. The Task of Social Hygiene. London, 1912. Ellis, H. The Problem of Race Regeneration. New York, 1911. Forel, A. The Sexual Question. New York, 1908. Galton, F. Inquiries into Human Faculty. New York, 1883. Galton, F. Natural Inheritance. London, 1889. Galton, F. Hereditary Genius. London, 1892. Galton, F. Essays in Eugenics. London, 1909. Goddard, H. H. The Kallikak Family. New York, 1912. Goldschmidt, R. Einfiihrung in die Vererbungswis- senschaft. Leipzig, 1911. Hacker, V. Allgemeine Vererbungslehre. Braun- schweig, 1912. Hertwig, O. Allgemeine Biologie. Jena, 1909. Johannsen, W. Elemente der exakten Erblichkeits- lehre, 2d Auf. Jena, 1913. Kellicott, W. E. The Social Direction of Human Evolution. New York, 1911. Lock, R. H. Variation, Heredity and Evolution. New York, 1911. REFERENCES 495 Loeb, J. Comparative Physiology of the Brain and Comparative Psychology. New York, 1900. Loeb, J. The Dynamics of Living Matter. New York, 1906. Loeb, J. The Mechanistic Conception of Life. Chicago, 1911. Loeb, J. Artificial Parthenogenesis. Chicago, 1913. Mctchnikoff, E. The Nature of Man. Chicago, 1903. Morgan, T. H. Heredity and Sex. New York, 1913. Mott, F. W. Heredity and Eugenics in Relation to Insanity. London, 1912. Nageli, C. Mechanische-Physiologische Theorie der Abstammungslehre. Miinchen, 1884. Plate, L. Vererbungslehre. Leipzig, 1913. Problems in Eugenics. Papers communicated to 1st International Eug. Cong. London, 1912. Punnett, R. C. Mendelism. London, 1911. Rignano, E. The Inheritance of Acquired Charac- ters. Chicago, 1911. Romanes, G. J. Darwin and After Darwin. Chi- cago, 1892. Saleeby, C. W. Parenthood and Race Culture. New York, 1909. Semon, R. Das Problem der Vererbungslehre er- worbener Eigcnschaften. Leipzig, 1912. Spencer, H. Principles of Biology. New York, 1883. Thompson, J. A. Heredity. Edinburgh, 1908. Thorndike, E. L. Animal Intelligence. New Y'ork, 1911. Treasury of Human Inheritance. London, 1912. Walter, H. E. Genetics. New York, 1913. 496 HEREDITY AND ENVIRONMENT Weismann, A. The Germ Plasm. New York, 1893. Weismann, A. Essays on Heredity. Oxford, 1889. Wilson, E. B. The Cell in Development and In- heritance. New York, 1900. Woods, F. A. Heredity in Royalty. New York, 1906. Monographs and Papers Bardeen, C. R. Abnormal Development of Toad Ova fertilized by Spermatozoa exposed to the Roentgen Rays. Jour. Exp. Zool., 4, 1907. Baur, E. Vererbungs und Bastardierungsversuche mit Antirrhinum. Zeit. f. induk. Abstam. 3, 1910. Boveri, Th. Zellen Studien. Die Entwicklung di- spermer Seeigel-Eier, etc. Jena, 1907. Broman, I. Ueber geschlechtliche Sterilitat. Wies- baden, 1912. Brooks, W. K. Are Heredity and Variation Facts? Address before 7th Internat. Zoological Congress, 1907. Castle, W. E. Studies of Inheritance in Rabbits. Carnegie Inst. Wash. Publ. 114, 1909. Castle, W. E. and Phillips, J. C. On Germinal Transplantation in Vertebrates. Carnegie Inst. Wash. Pub. No. 144, 1911. Cattell, J. McK. The Causes of the Declining Birth Rate. Proc. First National Conference on Race Betterment. Battle Creek, 1914. Conklin, E. G. Embryology of Crepidula. Jour. Morph. 13, 1897. Conklin, E. G. The Cause of Inverse Symmetry. Anat. Anz., 1903. Conklin, E. G. The Organization and Cell-Lineage REFERENCES 497 of the Ascidian Egg. Jour. Acad. Nat. Sci. Phila., 1905. Conklin, E. G. Experimental Studies on Nuclear and Cell Division. Ibid., 1912. Conklin, E. G. The Mutation Theory from the Standpoint of Cytology. Science, 21, 1905. Conklin, E. G. The Mechanism of Heredity. Sci- ence, 27, 1908. Conklin, E. G. Heredity and Responsibility. Sci- ence, 37, 1913. Correns, C. Zur Kenntnis der scheinbar neuen Merkmale der Bastarde. Ber. D. bot. Ges. 23, 1905. Davenport, C. B. Inheritance in Poultry. Car- negie Inst. Wash. Publ. 53, 1906. Davenport, C. B. Heredity of Skin Color in Negro-White Crosses. Carnegie Inst. Wash. Publ. 188, 1914. Davenport, C. B. Inheritance of Characteristics in Domestic Fowl. Carnegie Inst. Wash. Publ. 121, 1909. East, E. M., Hays, H. K. Heterozygosis in Evolu- tion and Plant Breeding. Bureau Plant Industry, Bull. 243, 1912. Fischer, E. Exper. Untersuchungen iiber der Verer- bung erworbener Eigenschaften. Allg. Z. f. Ento- mol. 6, 1901; 7, 1902. Gudernatsch, J. F. Feeding Experiments on Tad- poles. II. Amer. Jour. Anat. 15, 1914. Guthrie, C. C. Further Results of Transplantation of Ovaries in Chickens. Jour. Exp. Zool. 5, 1908. Guyer, M. F. Accessory Chromosomes in Man. Biol. Bull. 19, 1910. Harrison, R. G. Experimentelle Untersuchungen, etc. Arch. f. Mik. Anat. 63, 1903. 498 HEREDITY AND ENVIRONMENT Harshberger, J. W. Maize; A Botanical and Eco- nomic Study. Cont. from Bot. Lab. Univ. of Penna., 1893. Hering, E. On Memory and the Specific Energies of the Nervous System. Chicago, 1897. Hertwig, O. Neue Untersuchungen iiber die Wirk- ung der Radiumstrahlung auf die Entwicklung tierischer Eier. Sitz. d. Kgl. Preuss. Akad. d. Wissenschaften, 29, 1910. Hertwig, O. Keimesschadigung durch chemische Eingriffe. Ibid., 30, 1913. Hertwig, R. Ueber den derzeitigen Stand des Sex- ualitatsproblcms. Biol. Centralblatt 32, 1912. Hoppe, H. Die Tatsachen iiber den Alkohol, 4 Aufl. Miinchen, 1912. Huxley, T. H. Evolution and Ethics. Romanes Lecture, 1893. James, W. The Energies of Men. Science, v. 25, 1907. Jennings, H. S. Behavior of the Lower Organisms. New York, 1906. Jennings, H. S. Heredity, Variation and Evolution in Protozoa. Proc. Am. Philos. Soc. 47, 1908. Jennings, H. S. Experimental Evidence of the Ef- fectiveness of Selection. Amer. Nat. 44, 1910. Jennings, H. S. Heredity and Personality. Science, 34, 1911. Johnson, R. Marriage Selection. Jour. Heredity, 5, 1914. Jordan, D. S. The Human Harvest, Boston, 1907. Jordan, H. E. The Biological Status and Social Worth of the Mulatto. Pop. Sci. Monthly, 1913. Kammerer, P. Direkt induzierte Farbanpassungen und deren Vererbung. Zeit fur Ind. Abstl. 4, 1911. REFERENCES 499 King, H. D. Studies on Sex Determination in Am- phibians. Biol. Bull. 16 and 20. Jour. Exp. Zool. 12. 1909, 1911, 1912. Lang, A. Vorversuche zu Untersuchungen iiber die Varietatenbildung von Helix hortensis und nemo- ralis. Festschr. f. Hackel. Jena, 1904. Lillie, F. R. The Mechanism of Fertilization in Arbacia. Jour. Exp. Zool. 1914. MacDougall, D. T. Alterations in Heredity induced by Ovarial Treatment. Bot. Gaz. 51, 1911. MacDowell, E. C. Size Inheritance in Rabbits. Carnegie Inst. Wash. Publ. 196, 1914. MacDowell, E. C. Multiple Factors in Mendelian Inheritance. Jour. Exp. Zool., 1914. Macfarlane, J. M. Contributions to the History of Dionaea muscipula. Contributions Bot. Lab. University Pennsylvania, 1, 1892. McClung, C. E. The Accessory Chromosome, Sex Determinant? Biol. Bull. 3, 1902. Mendel, G. Versuche iiber Pflanzenhybriden. Verh. naturf. Ver. Briinn, 4, 1866. Montgomery, T. H. Human Spermatogenesis. Jour. Acad. Nat. Sci. Phila. 15, 1912. Morgan, T. H. A Biological and Cytological Study of Sex Determination in Phylloxerans and Aphids. Jour. Exp. Zool., 7, 1909. Mulsow, K. Der Chromosomencyclus bei Ancyracan- thus cystidicola Rud. Arch. f. Zellf., 9, 1912. Nettleship, E. Some Hereditary Diseases of the Eye. Trans. Ophthal. Soc. 29, 1909. Nilsson-Ehle, H. Einige Ergebnisse von Kreuzun- gen bei Hafer und Weizen. Bot. Notiser fiir 1908. Osborn, H. F. Cartwright Lectures on Contempo- rary Evolution in Man, Amer. Nat. 26, 1892. 500 HEREDITY AND ENVIRONMENT Pearl, R. The Mode of Inheritance of Fecundity in the Domestic Fowl. Jour. Exp. Zool. 13, 1912. Pearson, K. Tuberculosis, Heredity and Environ- ment. London, 1912. Pearson, K., Nettleship, E., Usher, C. Monograph on Albinism in Man. London, 1911. Plate, L. Bemerkungen iiber die Farbenrassen der Hausmaus und die Schreibweise der Erbformeln. Zeit. f. induk. Abstam. 6, 1912. Rosanoff, A. J. The Inheritance of the Neuro- pathic Constitution. Jour. Am. Med. Assoc. 58, 1912. Shull, G. H. Hybridization Methods in Corn Breed- ing. Am. Breeder's Mag. 1, 1910. Stevens, N. M. Studies in Spermatogenesis with Especial Reference to the "Accessory Chromo- some." Carnegie Inst. Wash. Publ. 36, 1905. Stockard, C. R. An Experimental Study of Racial Degeneration in Mammals Treated with Alcohol. Arch. Internat. Med. 10, 1912. Stockard, C. R. The Experimental Production of Various Eye Abnormalities, etc. Arch. f. ver- gleich. Ophthal. 1, 1911. Summer, F. B. An Experimental Study of Somatic Modifications and their Reappearance in the Off- spring. Arch. Entw. Mech. 30, 1910. Tennent, D. H. Studies in Cytology, I and II. Jour. Exp. Zool. 12, 1912. Tennent, D. H. The Dominance of Maternal or of Paternal Characters in Echinoderm Hybrids. Arch. Entw. Mech. 29, 1910. Tower, W. L. An Investigation of Evolution in Chrysomelid Beetles of the Genus Leptinotarsa. Carnegie Inst. Wash. Publ. 48, 1906. REFERENCES 501 Weeks, D. F. The Inheritance of Epilepsy. Prob- lems in Eugenics, 1. Whitman, C. O. Animal Behavior. Biol. Lectures. Woods Hole, 1899. Whitney, D. D. The Effects of Alcohol not in- herited in Hydatina senta. Amer. Nat. 46, 1912. Wiesner, J. . Die Elementar-structur und das Wachs- tum der lebenden Substanz. Wien, 1892. Wilder, H. H. Duplicate Twins and Double Mon- sters. Amer. Jour. Anat. 3, 1904. Wilson, E. B. Some Aspects of Cytology in Rela- tion to the Study of Genetics. Am. Nat., 1912. Wilson, E. B. Studies on Chromosomes. I-VIII. Jour. Exp. Zool. 2, 3, 6, 9, 13. Jour. Morph. 22. Winiwarter, H. Etudes sur spermatogenese humain. Archiv d. Biologie, 27, 1912. Wolff, C. F. Theoria Generationis. 1759. Woltereck, R. Beitrag zur Analyse der Vererbung erworbener Eigenschaften ; Transmutation und Prainduktion bei Daphnia. Verh. D. Zool. Ges., 1911. GLOSSARY ACCESSORY CHRO'-MO-SOME. An odd chromosome which is found in only half of the spermatozoa of certain animals; see "sex-chromosome." A-CHRO'-MA-TIN. The non-staining substance of the nucleus as contrasted with the chromatin. A-CHON'-DRO-PLA-SY. A condition in which the long bones cease to grow in length at an early age thus producing a dwarf with large body and head but short limbs. ACQUIRED CHARACTER. A character, the differential cause of which is environmental. ALTERNATIVE INHERITANCE. Galton's term for a doubtful kind of inheritance in which all characters are derived from one parent. In present use, Mendelian inheritance. AM'-NI-ON. One of the embryonic membranes of higher verte- brates. AM-PHI-OX'-US. One of the lowest and simplest animals hav- ing a notochord (backbone). AN-EN-CEPH'-A-LT. The condition of a brainless monster. ANIMAL POLE. That pole of an egg at which the polar bodies are formed. AN'-LA-GE. The embryonic basis of any developed part. A-OR'-TA. The great artery arising from the heart. AR'-CHI-PLASM. The deeply staining plasm surrounding the centrosome. AS'-CA-RIS. A genus of round worms which are intestinal parasites. AS'-CA-RIS meg-a-lo-ceph'-a-la. A parasite in the intestine of the horse. AS-CID'-I-AN. A "sea-squirt"; one of the lowest types having a notochord, or elementary backbone. 503 504 GLOSSARY AS'-TER. The radiating figure surrounding the centrosome in a cell. AS-SIM-I-LA'-TION. Conversion of food substances by an or- ganism into its own living substance. A-SYM'-ME-TRY. The condition where opposite sides are unlike. AT'-A-VISM. The condition in which an individual resembles a grandparent, or a more distant ancestor, more than one of the parents. BI'-O-PHOKES. The ultimate units of life (Weismann). BI'-VA-LENT CHRO'-MO-SOMES. A pair of chromosomes, one ma- ternal the other paternal, temporarily united. BLAS'-TO-COEL. The cavity within a blastula. BLAS'-TO-DER'-MIC VES'-I-CLE. A hollow sphere, formed from the segmented egg of a mammal, which becomes attached to or embedded within the wall of the uterus. BLAS'-TO-PORE. The mouth of a gastrula. BLAS'-TTJ-LA. A mass of cells, usually in the shape of a hollow sphere, formed by repeated divisions (cleavages) of an egg- BLENDING INHERITANCE. Galton's term for that kind of in- heritance in which the characters of the parents seem to blend in the offspring. BRACH-Y-DAC'-TY-LISM. The condition of having abnormally short fingers or toes. CELL. The fundamental unit of structure and function in all living things. CEN'-TRO-SOME. The body at the center of radiations in a dividing cell. CEPH'-A-LO-PODS. A class of mollusks which includes the squid, cuttle-fish and devil-fish. CER'E-BRAL GANO'-LI-ON. The brain of an invertebrate animal. CHARACTER. Any feature or property of an organism. CHOR'-DA. A cellular rod in vertebrate embryos which forms the basis of the backbone. CHOR'-DATE. A member of the highest phylum of the animal kingdom, including all animals having a chorda or back- bone. GLOSSARY 505 CHO'-RI-ON. A tough membrane around an egg secreted by .surrounding cells. CHRO'-MA-TIK. The deeply staining substance of the nucleus. CHHO'-MO-SOMES. Deeply staining bodies found in the nucleus at the time of indirect division. CII/-I-A. Minute protoplasmic threads on the surface of a cell which produce movements in the surrounding medium by waving back and forth. CLASS. The chief sub-division of a phylum. CLEAV'-AGE. The division of the egg cell after fertilization into many cells. CLEP-SI'-NE. A genus of leeches. COE'-LOM. The body cavity. CONTINUOUS VARIATION. A series of minute variations. CORRELATIVE DIFFERENTIATION. Differentiation due chiefly to the interaction of different parts of an organism. CRE-PID'-U-LA. A genus of marine gastropods. "CRISS-CROSS" INHERITANCE. Morgan's term for that kind of inheritance in whicn maternal characters are transmitted to sons and paternal ones to daughters. CTEN'-O-PHORE. A jelly-sphere; a member of a phylum of marine animals standing above the jelly-fishes. CY-CLO'-PI-A. A monstrosity in which both eyes have fused into a single one. CY-TOL'-O-GY. The science which treats of cells. CY'-TO-PLASM. The protoplasm of a cell outside of the nucleus. DAL'-TON-ISM. That form of color-blindness in which one is unable to distinguish red and green; usually limited to males. DAR' -WIN-ISM. The doctrine that evolution takes place through natural selection or the survival of the fittest. DETERMINANTS. The units of heredity (Weismann). DETERMINER. The differential cause or factor in a germ cell which determines the development of a character. DEX'-THAL SNAIL. The usual type of snail in which the shell coils from base to apex in a clockwise direction. DIFFERENTIATION. The process of producing specific parts or substances from a general part or substance. 506 GLOSSARY DI-HY'-BRID. The offspring of parents differing in two char- acters. DI-O-NAE'-A. An insect-catching plant, the "Venus Fly-trap." DIP'-LOID. The full number of chromosomes found in the ferti- lized egg and in all cells derived from this, except the mature germ cells. DOMINANT CHARACTER. A character inherited from one parent which develops to the exclusion of a contrasting character of the other parent. DROS-OPH'-I-LA. A genus of fruit-flies. DU'-PLEX FACTORS or CHARACTER. A condition where the de- terminers for a character are derived from both parents. E-CHI'-NO-DERMS. A phylum of marine animals which includes star-fishes and sea-urchins. E-COL'-O-GY. The science which deals with the relations of organisms to one another and to environment. EC'-TO-DERM. The outer layer of cells of an embryo which gives rise to epidermis, sense organs and nervous system. EM-BRY-OG'-E-NY. Early development of an egg leading to the formation of an embryo. EN'-DO-DEHM. The inner layer of cells of an embryo, which gives rise to the digestive cells of the alimentary system. EP-I-GEN'E-SIS. The doctrine that the germ is simple and homogeneous and that development consists in the for- mation of complex parts from the simple germ. EQUATION-DIVISION. An ordinary nuclear division in which each chromosome divides equally. EU-GEN'-ICS. The system of imp roving 'races by good breeding. EU-THEN'-ICS. The system of improving individuals by good environment. EX-O-GAS'-TRU-LA. A gastrula with the endoderm turned out instead of in. FACTOR. A specific germinal cause of a developed character. FERTILIZATION. The union of male and female sex cells. FLA-GEL'-LUM. A vibratile thread of protoplasm which serves as an organ of locomotion. FLUCTUATIONS. Variations which are not inherited. GLOSSARY 507 FOL'-LI-CLE CELLS. Nutritive cells surrounding an ovarian egg. FRATERNAL TWINS. Twins produced from different eggs and showing different hereditary characters. FUNCTIONAL ACTIVITY. Use. GAM'-ETE. The mature male or female sex cell. GANG'-LI-ON. A group of nerve cells. GAS'-TEO-COEL. The digestive cavity of the gastrula. GAS'-TRU-LA. A stage in development following the blastula, in which the embryo consists of an outer (ectoderm) and an inner (endoderm) layer of cells. GENES. Factors, units, elements of germ cells which condition the characters of developed organisms (Johannsen). GE-NET'-ICS. The science which deals with the origin of indi- viduals and particularly with heredity. GE'-NO-TYPE. The germinal type with all its hereditary pecu- liarities. "The fundamental hereditary constitution of an organism" (Johannsen). GERM-PLASM. The material basis of inheritance. GERM-TRACK. The cell-lineage of the germ cells in a develop- ing animal. GERMINAL UNITS. Hypothetical parts of germ cells which are supposed to have certain specific functions in development. HAE-MO-PHIL'-I-A. An abnormal condition in which the blood clots slowly. HAP'-LOID. The reduced number of chromosomes in the gametes. HEREDITY. The appearance in offspring of characters whose differential causes are in the germ cells. HERITAGE. The sum of those characters which are inherited by an individual. HET-ER-O-ZY-GO'-SIS. Hybridization ; cross-breeding. HET-ER-O-ZY'-GOTES. Hybrids resulting from the union of gametes which are hereditarily dissimilar. HO-MO-ZY'-GOTES. Pure-breds resulting form the union of gametes which are hereditarily similar. HY'-BRID. The offspring of parents which differ in one or more characters. 508 GLOSSARY IDENTICAL TWINS. Twins which have come from a single egg and which show identical hereditary characters. ID'-I-O-PLASM. The germ-plasm or inheritance material. INDUCTION. A modification of the first filial generation caused by the action of environment on the germ cells of the parental generation. INHERITED CHARACTER. A character the differential cause of which is in the germ. INSTINCTS. Complex reflexes involving nerve centers. INVERSE SYMMETRY. Having the right half of one asymmetri- cal individual equivalent to the left half of another. IRRITABILITY. Capacity of receiving and responding to stimuli. LA-MARCK'-ISM. The doctrine that evolution takes place through the inheritance of acquired characters. LOCALIZATION. The gathering together of particular sub- stances in definite parts of an egg or embryo. LOL'-I-GO. The squid, a genus of cephalopod mollusks. MAR-SU'-PI-ALS. A primitive group of mammals, including op- posums and kangaroos, which carry the young in a pouch. MAT-u-RA'-TfoN. The final stages in the formation of sex cells, characterized by two peculiar cell divisions. ME-RIS'-TIC VARIATION. Variation in the number of parts. MES'-EN-CHYME. Loosely scattered cells of the mesoderm. MES'-O-DERM. A layer or group of embryonic cells lying be- tween ectoderm and endoderm. ME-TAB'-O-LISM. Transformations of matter and energy within a living thing. MI'-CRO-PYLE. The minute opening in an egg membrane through which the spermatozoon enters. MI-TO'-SIS. Indirect nuclear division in which the nucleus is transformed into a spindle and chromosomes; the latter split and the halves move to the poles of the spindle where they form the daughter nuclei. MON-O-HY'-BRID. The offspring of parents differing in one character. MON'-O-TREMES. The lowest group of mammals, including the duck-bill and the spiny anteater. GLOSSARY 509 MOR-PHOL'-O-GY. The science which deals with structure and form. MUS'-CA. A genus of flies including the house-fly. MU'-TANT. A sudden variation or sport which breeds true. MU-TA'-TIONS. Inherited variations which are more or less striking. NEC-TU'-RUS. A large salamander; the mud-puppy. NEM'-A-TODE. A round-worm or thread-worm. NE'-HE-IS. A marine annelid, or ringed worm. NEURAL GROOVE. The groove on the dorsal surface of the embryo of a vertebrate which develops into the brain and spinal cord. NEURAL TUBE. A tube formed from the neural groove and giving rise to brain and spinal cord. NO'-TO-CHORD. The cellular rod which forms the basis of the backbone. NU'-CLE-US. The central organ of a cell, composed of chro- matin and achromatin. NULLIPLEX FACTORS or CHARACTER. A condition in which a character is absent because its determiner is found in neither parent. ON-TOG'-E-NY. Development of an individual. O'-O-CYTE. The ovarian egg before maturation (formation of polar bodies). O-O-GEN'-E-SIS. The development of an ovum from a primitive sex-cell. O-O-GO'-NI-A. The earliest generations of cells which produce ova; primordial egg cells. O'-O-SPERM. The fertilized egg after union of egg and sperm. ORDER. The chief sub-division of a class. ORGANIZATION. Differentiation and integration, i.e. different parts united into one whole. OR-GAN-OG'-E-XY. The formation of various organs of the body. OR-THO-GEN'-E-SIS. The doctrine that the course of evolution is definitely directed by intrinsic causes. 510 GLOSSARY O-VI-PAR'-I-TY. Young brought forth as eggs, i.e., in an early stage of development. O'-VULES. The female sex cells of flowering plants with the immediately surrounding parts. O'-VUM. The female sex cell. OX-Y-CHRO'-MA-TIN. That portion of the chromatin which does not form chromosomes. PAN-GEN'-E-SIS. The hypothesis proposed by Darwin that every cell of the body gives off minute germs, "gemmules," which then collect in the sex cells. PAR-A-ME'-CI-UM. A ciliated protozoan. PAR-THE-NO-GEN'-E-SIS. Development of an egg without pre- vious fertilization. PARTICULATE INHERITANCE. Gallon's term for that kind of in- heritance in which certain characters are derived from one parent and others from the other parent, i.e. Mende- lian Inheritance. PA-THOL'-O-GY. The science which deals with disease. PHE'-NO-TYPE. The developed type in which some of the her- editary possibilities are realized 1 while others remain un- developed. "Developed, measurable realities" (Johannsen). PHY-LOG'-E-NY. Evolution of a race or species. PHYL-LOX'-E-RA. A genus of plant lice. PHY'-LUM. One of the chief sub-divisions of the animal king- dom. PHYS-I-OL'-O-GY. The science which deals with function. PLAS'-TO-SOMES. Threads or granules in the cytoplasm which are colored by certain dyes. POLAR BODIES. Two minute cells which are separated from the egg in its two maturations divisions. PO-LAR'-I-TY. The condition where two poles of a body differ; in eggs the two poles are the animal (formative) and the vegetative (nutritive) . POL'-LEN. The male sex cells of flowering plants. POL-Y-DAC'-TYL-ISM. The condition of having more than the normal number of digits on hands or feet. POL-Y-HY'-BRID. The offspring of parents differing in more than three characters. GLOSSARY 511 PRE-FOR-MA'-TION. The doctrine that the fully formed organ- ism exists in the germ, and that development is merely its unfolding. PRE-IN-DUC'-TION. A modification of the second filial gener- ation caused by the action of environment on the germ cells of the parental generation. PRE-PO'-TEN-CY. The preponderance of one parent over the other in the transmission of hereditary characters. PRI'-MATES. The highest order of mammals, including monkeys, apes, and man. PRIMITIVE SEX CELLS. The earliest recognizable progenitors of the sex cells in development. PRO'-TE-IN. Complex organic substances containing nitrogen, e.g. white of egg. PRO-TE'-NOR. A genus of the true bugs. PRO'-TO-PLASM. The living material of an organism. PRO-TO-ZO'-A. The simplest animals, usually consisting of a single cell. PY-LO'-RUS. The narrow opening between stomach and intestine. RECESSIVE CHARACTER. An inherited character which remains undeveloped when mated with a dominant character. REDUCTION-DIVISION. That maturation division in which the number of chromosomes is halved. REFLEXES. Relatively simple, automatic responses. RESPONSE. Any activity of an organism called forth by a stimulus. REVERSIONS. The sudden reappearance of long-lost racial characters. SEGREGATION. The separation of dominant and recessive char- acters in the offspring of hybrids. SELF DIFFERENTIATION. Differentiation due chiefly to intrinsic causes. SENSITIVITY. Capacity of receiving and responding to stimuli. SEX CHRO'-MO-SOME. The "odd" or accessory chromosome which is supposed to determine sex. SEX-LIMITED. Any character which is found in one sex only. 512 GLOSSARY SEX-LINKED. Any character, the determiner of which is as- sociated with the determiner of sex. SIMPLEX FACTORS or CHARACTER. A condition where the de- terminer for a character is derived from one parent only. SIN'-IS-TRAL SNAIL. A type of snail in which the shell coils from base to apex in an anti-clockwise direction. SO'-MA. The body as contrasted with the germ cells. SO-MAT' -ic. Pertaining to the body, as contrasted with "germi- nal" pertaining to the germ cells. SO'-MA-TO-PLASM. The body-plasm as contrasted with the germ-plasm. SO'-MITE. A segment of the body of a segmented animal. SPER-MA'-TO-CYTES. The mother and grandmother cells of spermatozoa. SPER-MA-TO-GEN'-E-SIS. The development of a spermatozoon from a primitive sex cell. SPER-MA-TO-GO'-NI-A. Primordial sperm cells. SPER-MA-TO-ZO'-ON. The mature male sex cell. SPINDLE. The nuclear division figure. SPI'-REME. A coiled thread of chromatin which appears in the nucleus at the beginning of division. SPI-RIL'-LA. A spiral type of bacteria. STEN'-TOR. A ciliated protozxmn. STER-E-O-I'-SO-MERES. Molecules having different properties dependent upon varying spacial relations of their con- stituent atoms. STIM'-U-LUS. Anything acting on an organism which calls forth a response. STY-E'-LA. A genus of Ascidians. SYM'-ME-THY. The condition where opposite sides or poles are alike; bilateral, having equivalent right and left sides. SYN-AP'-SIS. The conjugation of maternal and paternal chro- mosomes preceding the maturation divisions. SYN-DAC'-TYL-ISM. The condition of having webbed fingers or toes. TE-NEB'-RI-O. A genus of beetles, the larva of which is the common meal worm. GLOSSARY 513 TER-A-TOL'-O-GY. The science which deals with monstrous or abnormal forms. TET'-RADS. Bivalent chromosomes which appear 4-parted in the maturation divisions. TO-TIP'-O-TENCE. The capacity of a cleavage cell to give rise to a whole animal. TOX'-IN. A poisonous substance particularly such as is pro- duced by bacteria. TRI-HY'-BRID. The offspring of parents differing in three char- acters. TROPH'-O-BLAST. The outer layer of the blastodermic vesicle of a mammal. TRO'-PISMS. Automatic movements of organisms toward or away from a source of stimulus. UNIT CHARACTER. A character which is inherited as a whole and cannot be sub-divided. VEGETATIVE POLE. The pole of an egg opposite the polar bodies. VIL'-LI. Processes which grow out from the embryonic mem- branes of a mammal and connect it to the walls of the uterus. VI-TEL'-LIKE MEMBRANE. A delicate membrane around an egg secreted by the egg itself. VIV-I-PAR'-I-TY. Young brought forth "alive," in an advanced stage of development. ZY'-GOTE. The product of the union of male and female sex cells. INDEX Proper names and titles of sections are in small capitals; page references to illustrations in italic numerals. Aborigines of Australia 402 New Zealand 402 North America 402 Pacific Islands 402 South America 402 Tasmania 401 West Indies 402 "Accessory" chromosome, 140, 141, 143, 144, 145, 166, 167, 271-277 Achondroplasy, 200, 293, 294 Achromatin, 109, 113 differential distribution, 184, in cell body, 181 ACQUIRED CHARACTERS, INHERI- TANCE OF, 334-351 Darwin on, 335 Lamarck on, 334 Weismann on, 335 definition of, 336, 337 general objections to, 338 specific objections to, 339- 347 Adaptive responses, 55, 78 Adrenal gland, fed to tadpoles, 326 African negro, 402, 407 in Jamaica, 417 in U. S., 417 Age of human race, 398 Albinism, 289, 291, 292 Alcoholism, 206, 295, 450 cause of sterility, still- births, malformation, dwarfs, 311, 312, 313 induction effect on rotifers, 349 influence on germ cells, 311 Alkaptonuria, 293 Alpine plants, non inheritance of acquired characters, 345 "Alternative" inheritance, 208 Alternatives in development, 462, 463 Amalgamation of races, 402, 416-419 American men of science, fami- lies of, 4?5 AMPHIOXUS, cleavage and differ- entiation, 119 cleavage and gastrulation, 25, larvae, 27, 29 isolated cleavage cells, 314, S15 Ancestors, number of, 216-218 Ancestry, pride of, 429 ANCYRACANTHUS, oogenesis, 134, spermatogenesis, 132 Andalusian fowl, Blue, 266 Anencephaly, 325 Animal pole of egg, 167 Annelid type of egg, 178 Ants and bees, 440, 483 Artificial limitation of fami- lies, 437, 438 Artificial parthenogenesis, 314 ARTIFICIAL SELECTION, 376 chief factor in production of domestic races, 376 creates nothing, 377-380 isolates pure lines, 378, 379 lacking, 409, 411, 412 methods of, 376, 377 results of, 377-380 ASCARIS, fertilization of, 112 515 516 INDEX "germ track," 126, 127 sex differentiation in, 144. Ascidian egg, 119, 120, 124, 168, 317, 319, 320, 322 type, 178 ASSHETON, cleavage of egg of sheep, 23 Aster, 109, 111 Astral radiations, 110 Atavism, 209 ATHENS, 406, 407 Athletes, prize, 415 Athletics, educational value of, 476, 477 ATTICA, illustrious men of, 405- 407 Automaton, 459, 461 Backbone, development of, 28, 29 "Back cross," ratios of, 237, 238 Bacteria, reactions to light, 49 Baldness, inherited, 203 BALZAC, heredity a maze, 297 Barbarism, 363, 396, 411, 486 BARDEEN, X-rays on sperma- tozoa, 311, 496 BATESON, Blue Andalusian, 266 brachydactyl hand, 292 "homozygote and heterozy- gote," 228 on Mendelism, 225, 493 BATESON and PUNNETT, on sweet pea hybrids, 256, 257, 258 . BATTR, factors for flowers of Antirrhinum, 259 induction effects of poor soil, 349, 493, 496 Beans, pure lines of, 197, 205 Bees, and Ants, 440, 483 influence of food on devel- opment, 326 workers, queens, drones, 326 BEETHOVEN, 473 Behavior, dogs, cats, monkeys, fish and frog, 465 lower organisms, 44 modifiability of, 68 Paramecium, 61-63, 66 plasticity of, 71, 464 rigidity of, 71 test of psychical processes, 48 worms, star-fish, Crustacea, vertebrates, 63, 64, 66, 70, 71 BERKELEY, BISHOP, 446 "Biophores" of Weismann, 100 Birthrate and deathrate, nor- mally equal, 432 both decreasing, 433, 434 decreasing most in best families, 434 in Massachusetts, 435 Bivalent chromosomes, 133 Blastula, 25, 26 "BLENDING" INHERITANCE, 208, 280, 282-287 in length of ears in rab- bits, 285 in length of skull in rab- bits, 285, 286 in skin color of mulatto, 282-285, 88 "Blood lines," 379 BOND, negro X white cross, 288 BOULE, Chapelle - aux - Saints skull, 397 BOVERI, chromosomes differ in value, 156, 165 dispermic eggs, 313, 496 Brachydactylism, 199, 292, 293 Brain, development, 28 size and weight, 472, 473 Breeder, methods of, 416 BROMAN, death of families, 436 496 BROOKS, 214, 496 Buddhistic belief in transmigra- tion, 40 BURBANK, new combinations of characters, 381 mutations, 384 INDEX 517 Canary birds, fed on red pep- per, 326 Capacity, greater than realiza- tion, 471, 472 Captivity, cause of infertility, 436, 437 CASTLE, 493, 496 factors for coat colors of rabbits, 259 recombinations o f charac- ters, 381, 382, 883 size in rabbits, 285-286 CASTLE and PHILLIPS, trans- planted ovaries of guinea- pigs, 342-^, 346 Cataract, hereditary, 199, 295 CATTELL. birthrate of college graduates, 431, 496 families of scientists, 435 Cause and effect, universality of, 446, 447 Causes, natural vs. final, 164 Celibacy, 409, 431 Cell characters inherited, 199 Cell division, 81, 24, 110, 112, 113, 114, 116, 120, 122 differential, 119, 122, 183- 186 non-differential, 122, 183- 186 significance of, 122, 123, 125, 126 Cell-Lineage, diagram of, 94 CELLULAR BASIS OF HEREDITY, 89 Centrifuged eggs, 321, 322 Centrosomes, 109 equal division of, 123, 184 Chances, definition of, 462, 463 infinity of in development, 425, 426 CHARACTERS, developed not transmitted, 351 individual, 196 inheritance of acquired, 334-351 inherited, definition of, 336, 337 latent, 209 new in evolution, 388, 394, 395 not independent, 193 patent, 209 racial, 195 CHILD, on chromosomes, 163, 164 Choice of alternatives, 466 j Chorea, 295 Chromatin, 24, 109 granules, 110 Chromomeres, equal division of, 184 Chromosomes, 24, 111, 113 abnormal distribution, 311, 313, 391, 392 accessory, 140 bivalent, 133 conjugation of, 131 daughter, 113 diploid, 137 distribution, 115 division, 111, 112, 123, 125, 184 haploid, 137 identity, 113 individuality, 115 maternal and paternal, 117 number of, 111, 145-147 "odd," 140 reduction of, 136 seat of factors, 164-167 shuffle and deal of, 158-160 tetrads, 135 X and Y, 143, 166 Civilization, means good en- vironment, 304 vs. heredity, 362 will it endure, 396, 486, 401 Classes, hereditary, 413,' 414 exclusive, 415 CLEAVAGE, of egg, 24, 25, 26 AND DIFFERENTIATION, 110- 126 differential, 122 non-differential, 122 significance of, 122, 123, 126 518 INDEX Cleavage cells, differentiation of, 26 isolated, development of, ' 314-322 CLEPSINE, behavior of, 68 Coeducation, 429, 430 Cold, induction effect on Daph- nia, 349 induction effect on mice, 349, 350 Coloboma, 200, 296 Color, of skin, hair, eyes, 197, 291, 889', 292 Color-blindness, 275-278 CONSCIOUSNESS, 73-76 continuity of, 74 loss of, 75 subconscious, 73 CONTROL OF, alternatives, 466 heredity and development, 5, 367 HUMAN EVOLUTION, 403 meaning of, 461 nature, 6 phenomena, 367, 461 self, 461 CORRELATIONS OF GERM AND SOMA, 162-179 "Correlative differentiation," 331, 332 CORRENS, 493, 497 rediscovery of "Mendel's Law," 224 on Mirabilis, 231, 232, 234, 249, 265 Creationism, 41 Creative Synthesis, 37, 84, 180 CREPIDULA, maturation and fer- tilization, 106, 107 individuality of germ nuc- lei, 116 exogastrula of, 324 Cretin, 294, 331 Criminality, 295, 445 CTENOPHORE, egg, 178 CULTIVATED PLANTS, 367, 368 number of species, 368 Culture, grades of, 396 CUVIER, 473 Cyclopia, 325 CYTOPLASMIC CORRELATIONS, 167 differentiations, 180 inheritance, 175-177 localization, 123 movements, 117 Daltonism, sex-linked, 275, 216, 277, 278 DAPHNIA, effect of cold on, 349 DARBYSHIRE, 493 DARWIN, hypothesis of pangen- esis, 92 on domestic pigeons, 368, 369, 370 inheritance of acquired characters, 335 prepotency, 223 reversion, 222, 223 "sports," 210 .zeal, 472 organism a microsome, 187 theory of Natural Selec- tion, 377, 494 Daughter nuclei, 24, 113 DAVENPORT, degrees of relation- ship, 217 extra toe in fowls, 267 inheritance of skin color, 283-285 Mendelian inheritance in man, 290 transplanted ovaries, 342 "weakness with strength," 426 white X black leghorns, 267 494, 497 DAVENPORT and WEEKS, epi- lepsy inherited, 206 Deaf-mutism, 200, 296 Death, of families, 434-439 Deathrate, declining, 432-435 Declaration of Independence, 303 INDEX 519 Decline of families and nations, 487 Defectives, growing burden of, 411 alarming increase of, 420 Defects, educational influence I of, 356 Democracy and human equality, 304 DESCARTES, 303 "Determinants" of Weismann, 100, 255 Determiners, 101 combinations of, 255 differential causes, 254 DETERMINISM, and RESPONSIBILITY, 443 definition of, 460 not FATALISM, 460 not predeterminism, 460 of ENVIRONMENT, 453-459 of HEREDITY, 44T-453 of personality, 459 scientific, 460 Development, a series of re- sponses, 327, 457 alternatives in, 462 definition of, 103 is transformation not new formation, 161 mosaic, 333 not reversible, 462 of function, 36 of personality, 7, 77, 460 potentialities "of, 454, 455 physiology of, 307 various aspects of, 76, 77 viviparous, 18, 19 DEVELOPMENT OF BODY, 8 or MIND, 39-41 DEVELOPMENTAL RESPONSES, 310- 327 AFTER FERTILIZATION, 314 BEFORE FERTILIZATION, 310 DURING FERTILIZATION, 313 DE VRIES, action of selection, 377, 380 fluctuations, 211, 212 induction effects of poor soil, 349 intra-cellular pangenesis, 182 "mutation theory," 211 mutations, 211, 212 Oenothera mutants, 393, 348 on nuclear control of differ- entiation, 182 pangenes, 100 rediscovery of "Mendel's Law," 224, 494 Diabetes, 293 Differential division, of Cyto- plasm, 126 of cells, 119, 122, 183-187 Differentiation, 37 "correlative," 331, 332 definition of, 103 due to interaction of cell parts, 163, 180, 181, 182 measure of, 186 nuclear control of, 181, 182 "self," 332, 333 Dihybrid, 239, 241, 242, 244 Dimples, inheritance of, 197 DIONAEA, reactions of, 56, 58 Diploid number of chromo- somes, 137 Disease, inheritance of, 200, 202 slight resistance to, 204 Dislocation of organs in centri- fuged eggs, 321, 322 Dispermic eggs, 313 Divines, poor health, 357 Division period, 128 Dogs, different races, 368 psychological characters in- herited, 204 DOMESTIC ANIMALS, 367-374 degree of change, 368 how produced, 375-377 number of species, 367 progenitors, 367, 368 regressive mutants, 394 520 INDEX DOMINANCE, MODIFICATIONS OF, 265 Blue Andalusian, 266 echinoderm hybrids, 268 extra toe in fowls, 26T in red x white Mirabilis, 265 nature of, 278 not fundamental, 279 plain x banded snails, 266 red X white cattle, 266 sex-limited characters, 270 sex-linked characters, 270- 278 white X black leghorns, 267 Dominant characters, 227 "extracted," 230 ratio to recessive, 233 DONCASTER, 494 Double monsters, 315, 316, 322, | 328 DRIESCH, 333, 494 DROSOPHILA, rapid breeding of, 290 sex-linked characters, 166, 271, 272, 273, 275 DRYDEN, 206 Duplex Characters, 249 Duty, 443, 459 of science, 480 Dwarfs, true, 293, 294 caused by alcohol, 312 Dynamic equilibrium, 10 Ear, development, 28 EAST, heterozygosis, 384, 385, 386, 497 ECHINODERM type of egg, 178 Ectoderm, 25, 27, 28 Education, and heredity, 428 i definition, 354 good and bad, 354, 356, 357 habit formation, 457 limiting activities, 356, 357 more potent in man, 354 needs of 475 possible improvements, 489 Egg and sperm, hereditary in- equality of, 176 Egg nucleus, 16, 24 Egg organization, types of, 178 ELLIS, 494 ELSBERG, plastidules, 100 Emboitment, 81 EMBRYOGENY, 26 Embryology, experimental, 307 Embryonic differentiation, pro- cesses in, 179 Embryos, double, 315, 316, 322, 323 dwarf, 315 half and three quarter, 317, 319 Endoderm, 25, 27, 28 "Energies of Men," 472 ENGELMANN, 49 English sparrow in U. S. 432 Engrammes, 348 Environment, acting at sensi- tive period, 375 definition, 307 direct action on germ cells, 351, 348 and education, 360 good and bad, 355, 356, 357, 475, 476 influence in producing new races, 375, 376 influence on ontogeny, 303, 305 influence on phylogeny, 302, 305 possible improvements, 489 social institutions and, 304 Epidermolysis, 293 Epigenesis, 81, 83, 161, 180, 452 Epilepsy, 205, 206, 295 Equality of Man, 303, 448 ETHICAL OBLIGATION, 484 Ethics, 491 Eugenicist, methods of, 416 Eugenical rules as to defects, recessive, 421, 422 INDEX 521 serious, 426-428 slight, 426 EUGENICS, 410-440 contributory, 428-431 declining birthrate, 431-440 definition of, 412 ideals, 412-419 negative, 419-423 only hope, 449 positive, 423-428 Problems in, 495 EUTHENICS, 352 Evolution, control of, 403, 404 experimental, 305, 395 progressive, 400 promotion of, 403, 488, 491 requires new characters, 388, 394, 395 retrogressive, 400 EVOLUTION OF MAN, 396-403 contemporary, 398 control of, 403, 404 future, 399, 400, 412 intelligence in, 403, natural selection in, 402 prehistoric, 398 Exogastrula, 824 Experience, factor in behavior, 464 learning by, 65, 465 Experimental medicine, 5 EXPERIMENTAL STUDY OF IN- HERITANCE, 222, 224 Eyes, development, 28 color, 197, 291 lacking, 325 fused together, 325 Facial features, inheritance of, 197 German type, 291 Hapsburg type, 291 Jewish type, 291 FACTORS OF DEVELOPMENT, 79-86 Factors, added in progressive mutations, 394 chemical comparisons, 394, 395 definition of, 101 differential, 264 distribution in maturation and fertilization, 262 dominant and recessive, not modified by union, 343 drop out in regressive mu- tations, 394 extrinsic and intrinsic, 85 for color developers, 256 of rabbits and mice, 259, of sweet peas, 256, 257, 258 for pigment, 256 location in cell, 261, 262, 263, 264 Mendelian, 264, 265 multiple, 281-287 nature of, 260 no formation de novo, 395 origin of new, 394, 395 relations to characters, 255, 256 sex determining, 265 FAHLENBECK, noble families of Sweden, 436 FARADAY, 474 Fat stains, effects on next gen- eration, 350 "Fate of part function of po- sition," 333 of organization, 334 Fecundity, inherited, 204 Feeble-mindedness, 205, 206, 295 Feminist movement, 484 Fertility, of lower types, 411 FERTILIZATION, 15, 16, 107-110 heterogeneous, 313 "Fewer and better children," 439 FISCHER, mutations of insects, 348, 497 Fluctuations, 211, 212, 389 Food, influence on development in tadpoles, canaries, bees, 326, 327 522 INDEX FOOT and STROBE LL, on chromo- somes, 163, 164 on sex-limited characters, 274 FOREL, 494 effect of alcohol on germ cells, 313 FORMATION OF SUBSTANCES IN CELLS, 180 FORMULAE, INHERITANCE, 244, 246, 247 Fowls, races of, 371, 372, 373 transplanted ovaries, 341, 342 FREEDOM, and determinism, 460 i birth and growth of, 464 definition of, 466 development of, 465 from reproduction, 485 greatest in man, 465 ' not absolute, 459 not uncaused activity, 466 of action, 72 of individual, 414, 443, 483 of society, 482 Friedrich's Disease, 295 Frog, behavior of, 465 double embryos, 315, 316 Function and structure, corre- lated, 202 FUNCTIONAL ACTIVITY, 327 in human development, 353 GAGER, radium on nuclear di- vision, 311 GALTON, age of marriage, 420, 431 "Ancestral Inheritance," 215, 216, 223 artistic faculty, 192, 215 characters, 192 definition of eugenics, 412 diseases, 192, 215 eugenical policy, 419, 420 eye-color, 192, 215 "Filial Regression," 218- 220, 223 genius inherited, 206, 215 heredity vs. civilization, 361 intermarriage of scholars, 415 kinds of inheritance, 208 nature and nurture, 301 on Ancient Greeks, 405, 407 on identical twins, 358 pioneer in heredity, 193 poor health of divines, 357 religious significance of evolution, 491 on "sports," 210, 211 statistical study of inheri- tance, 214-223 stature, 192, 196, 215 weight of seeds, 192 Gamete, 13 Gardener, methods of, 416 Gastrula, 25, 27 GATES, Oenothera chromosomes, 392 GAUSS, 473 "Gemmules," of Darwin, 92, 100 Generalized types, 413, 415 Generations, parental and fil- ial, 228, 230 symbols of, 231 Genes, 101 Genius, and physical defects, 357 hereditary, 206 unstable nervous organiza- tion, 206 Genotype, 96, 241, 243, 245, 248, 337, 381 Geographical isolation, 416 GERMAN EMPEROR, number of ancestors, 217 GERM CELLS, 8, 104 alive, 9 complexity of 187 possibilities determined in, 448 potential personalities in, 438 reactions of, 464 INDEX Germ nuclei, 24 individuality of, 115, 116 Germ plasm, in nucleus, 123 Theory of Weismann, 96, j 9T, 335, 336 Germ vs. Soma, 96 "Germ track," diagram of, 94 GERMINAL CONTINUITY, 92-97 Glandular secretions, effects of, i 329-331 Glaucoma, 296 GODDAHD, feeble-mindedness in- j herited, 206, 494 GOLDSCHMIDT, 494 Gonia, 128 Grafts, not modified by stock 341, 342 Great men, in crises, 4T4 GREECE, decay of, 485, 486 GREEKS, ancient, 405-408 Growth period, 128 GUDERNATSCH, effects of food on tadpoles, 326, 497 Guinea-pigs, recombinations of characters, 381, 382, 383 transplanted ovaries, 342- 1 344, 346 GUTHRIE, transplanted ovaries, 341, 497 GUYER, on chromosomes of man, 147, 497 Habits, definition, 354 good and bad, 354-356, 464 HACKER, 494 HAECKEL, plastidules, 100 HAEMOPHILIA, 203, 275, 296 Hair, color, 291 form, 288, 291 Half castes, of Australia, 417 of New Zealand, 417 HANSEN, mutations of yeast, 348, 391 Haploid number of chromo- somes, 137 Hardship, educational value of, 355, 475 HARRIS, induction effects of poor soil, 349 HARRISON, on transplanted limbs, 333 graft of tadpoles, 341, 342, 497 HARSHBERGER, 498 HARVEY, epigram, 9 epigenesis, 81 HATSCHEK, cleavage and gas- trulation of AMPHIOXITS, 25 larvae of AMPHIOXTJS, 27, 29 Hereditary lines, interwoven, 488 HEREDITARY RESEMBLANCES AND DIFFERENCES, 193, 194, 207- 214 Heredity, and memory, 347 and variation, 194, 212 control of, 387 definition of, 89, 90, 103 includes assimilation, etc., 163 mechanism of, 105 ' more potent than environ- ment, 438 possible improvements, 490 theories of, 105 usually unchanged by en- vironment, 437-447 HEREDITY AND DEVELOPMENT, 102-104 HEREDITY AND ENVIRONMENT, 85, 86, 302-306 HEREDITY, ENVIRONMENT, TRAINING, 357-359 HEHING, Organic memory, 59, 498 Heritage, definition of, 103 HERTWIG, O., discovery of ferti- lization, 107 human ovum, 11 idioblasts, 100 influence on germ cells of X-rays, radium, chemi- cals/drug habit, 311, 313, 498 HERTWIG, R., modification of sex ratio, 148-150, 498 524 INDEX Heterozygosis, 384, 385, 386, 387 Heterozygotes, 228, 230, 241, 243, 245 Hindu Dwarfs, 294 HIPPOCRATES, 91 HOMO SAPIENS, 396, 402, 412 NEANDERTHALENSIS, 397 Homozygotes, 228, 230, 241, 242, 245 "Homunculus," 80 HOPPE, Effect of alcohol on germ cells, 312, 498 Human embryo, development, 33, 35 HUMAN EVOLUTION, CONTROL OF, 403 slow, 438 Human faculties, definition, 354 Human Heredity, no improve- ment in, 405-410 Human oosperm, early develop- ment, 31 ovum, 11, 14 spermatozoa, 14 Humidity, influence on muta- tion, 310 Huntington's Chorea, 295 HUXLEY, Evolution and Ethics, 361, 498 Hybrid races, quality of, 418 Hybridization, human, 416, 417, 418 Hybrids, increased vigor, 384 Hypertrophied heart, not in- herited, 338, 340 Hypophysis, effects on de- velopment, 331 Hypotrichosis, 293 Hysteria, 206 295 Ideals, individual and social, 413, 414 Identity, sense of, 75 "Idioblasts" of Hertwig, 100 Idioplasm, of Nageli, 97 Immigration, 407, 418, 419 laws, 421 Impulses, conflicting, 465 Inbreeding, 414, 415, 416 INDIVIDUAL, AND RACE, 482 minor unit, 488, 489 INDIVIDUAL CHARACTERS, 196 Morphological, 196 Physiological, 202 Psychological, 204 Teratological, 199 Individuals and their charac- ters, 191 "Induction," effect of colored soil, 350 poor, soil, cold, alcohol, 349 not inherited, 351 Inequality of all men, 448 Infancy, prolonged in man, 353, 456 Infertility, causes of, 436 Inheritance, "alternative," SOS "blending,"* 208 of baldness, 203 cell characters, 199 dimples, 197 facial features, 197 fecundity, 204 genius, 206 instincts, 204 intellectual capacity, 205 left-handedness, 204 longevity, 202, 203 moral tendency, 205 obesity, 203 "particulate," 208 pathological characters, 199-202 physiological characters, 202 psychological characters, 204-207 sex-limited and sex-linked, 209 stature, 196, 218, 219, 220 temperament, 205 teratological characters, 199 through cytoplasm, 175-177 tuberculosis, 201, 202 will, 205 INHERITANCE FACTORS, 252 Inheritance material, 97 seat of, 162 INDEX 525 Inheritance units, 99, 102 Inhibition, 68, 464 Insanity, 205, 206, 295 INSTINCTS, 52-56, 78 altruistic, 467 inherited, 204 origin of, 56 reproductive, 484 INTELLECT, 59-66 Intellectual capacity, inherited, 205 genius, 291 mediocrity, 291 Intelligence, factor in control, 461 in evolution of man, 403 | Interaction of parts, 328-334 Intra-cellular pangenesis, 182 INVERSE SYMMETRY, 170-174 Irritability, 12, 36 ISOLATION OF SUBSTANCES IN I CELLS, 183, 185 in protozoa, 185 JAMES, WILLIAM, 472, 498 JENNINGS, action of selection, 378 behavior of Paramecium, 62 behavior of Stentor, 68 inheritance of size in Para- mecium, 198 on Galton's laws, 221 on potential personalities, 474 rapid breeding of Para- mecium, 290 training of star-fish, 69, 498 JEROME, St., 41 Jews, mixture with Gentiles, 417 JOHANNSEN, action of selection, 377, 378 genotype and phenotype, 96 inherited weight of seeds, 197 "pure lines," 378, 494 JOHNSON, marriages of college women, 430, 431, 498 JORDAN, D. S., 498 JORDAN, H. E., 498 KAMMERER, effects of colored soil on salamanders, 350, 498 KEIBEL, development of human embryo, 31, 3S, 35 KELLICOTT, 494 Keratosis, 293 KING, modification of sex ratio, 149, 150, 499 KORSCHELT and HEIDER, Sym- metry of egg of Musca, 169 LAMARCK, on inheritance of ac- quired characters, 334 LAMARCKIAN HYPOTHESIS, 347, 348 Lamarckism, 38 LANG, snail hybrids, 266, 267, 499 Laws on Eugenics, 420, 421 Learning by experience, 65, 465 Left-handedness, inheritance of, 204 Lens, cataract, 199, 296 development of, 332 displaced, 296 weight of, 199 LEPTINOTARSA, selection in 379 Life, artificial production of, 302, 304 conditions limited, 453 definition of, 9 maze of, 463 LILLIE, fertilization of NEREIS, 17, SO, 21 on fertilizin, 154, 499 Limbs, transplanted, 332, 333 LINCOLN, 424 LOCALIZATION PATTERN, 172 in eggs o-f ctenophore, flat- worm, echinoderm, anne- lid-mollusk, chordate, 172, 178 Localization of substances in cells, 185 LOCK, 494 LOEB, J. Artificial partheno- genesis, 108, 152, 495 526 INDEX reflexes, 55 i tropisms, 54 Logic, as test of truth, 451 LOLIGO, symmetry of egg, 169 ! Longevity inherited, 202, 203 Luxury, cause of infertility, 436, 437 in education, 475, 476 , MACFAHLAXE, on Dionaea, 56,1 499 Me CLUXG, on sex determina- tion, 141, 166, 499 MAC DOUGALL, influence of chemicals on ovules, 311, 499 MAC DOWELL, size in rabbits, 285-287, 499 Me GREGOR, Restoration of Pithecanthropus skull, 397 Male babies, greater mortality, 150 MALTHUS, theory of, 420 Man, controls destiny, 399 dominant races of, 401 evolution of, 396-403 extermination of, 401, 402 extinct types of, 396, 897 freer than animals, 465 mongrel race, 425 place in nature, 3 prehistoric, 398 races of, 400 species of, 396, 397 value of races of, 400 MAORIS of New Zealand, 402 Marriage, age of, 420, 431 selection, 426-428 Marsupials, 32 MASSART, reactions of SPIRILLA, 51 Materialism, 44 "Maternal impressions," 34 Matter and mind, 44 MATURATION PERIOD, 135 divisions, 135, 137 Maze, of heredity, 214, 297 life, 463 MECHAXISM OF DEVELOPMENT, 179 MECHANISM OF HEREDITY, 151 Mechanistic hypothesis, 479 Mediocrity, tendency to, 218 MEISCHER, On stereoisomeres of albumin, 155 MEMORY, 56-59, 78 MENDEL, abbot of Brlinn, 224 dominant and recessive characters, 227-228 dominant: recessive ratios, 228-245 experiments on peas, 193, 224, 226, 499 inheritance formulae, 246, 247 inheritance units, 255 method of work, 225 neglect of discoveries, 225 purity of germ cells, 234, 235 MEXDELIAN ASSOCIATION AND DISSOCIATION, 386-388 Mendelian factors and chro- mosomes, 165, 166, 262, 263, 264, 265 MENDELIAX INHERITANCE IN MAX, 288-296 Table of, 291-296 MEXDELIAN PRINCIPLES, 250 DOMINANCE, 251 MODIFICATIONS AND EXTEN- SIONS, 252 SEGREGATION, 251 UxiT CHARACTERS, 250 Mendelian ratios, simple, 228, 230, 231, 232-V,m "back cross," 237, 238 monohybrid, 340, 244 dihybrid, 239, $41, 242, 244 trihybrid, 243, 244, 245 dominant-recessive, 233 departures from, 280, 281, 282 MEXDELISM, 224-251, 297 MEXDELSSOHN, reactions of Paramecium, 53 Meniere's disease, 295 Mentality, influence of educa- tion,' 303 INDEX 527 Mesoderm, 27, 28 Metabolism, 12, 36 METCHINIKOFF, disharmonies in man, 361, 495 Metempsychosis, 40 Microscopic particles, smallest visible, 99 Mind and body, 45 Mind, development of, 42, 43 MIHABILIS, white-red cross, 231, 232, 234, 249, 265 Mitosis, 21, 24, 110, 112, 113, 114, 115, 116, 120 significance of, 122, 123,! 125, 126 "Mneme" theory, 347, 348 Modifiability of behavior, 68 Molecular constitution, stere- oisomeres, 155 Molecules, largest known, 99 Monasticism, 409, 430, 431 Monohybrid, 228, 236, 240, 244 Monotremes, 32 Monstrous development, 309, 454, 455 cause of, 310 MONTGOMERY, on Chromosomes of man, 147, 499 Moral qualities inherited, 205 MORGAK, mutations of insects, 348, 391, 495, 499 sex chromosome, 166, 167' sex determination in Phyl- loxera, 150 . sex-linked inheritance, 271, 212, 274, 275, 276, 277, 278 rapid breeding of Droso- phila, 290 Morphological characters, 196 tests, 39 Mosaic development, 333, 318 Moth and flame, 464 MOTT, insanity inherited, 206 495 Mouse, maturation and fertili- zation, 114. Movements, within eggs and cleavage cells, 50, 106, 110, 117, 183. effects of stopping, 328 random, 55 of spermatozoa, 49, 50 Mulattoes, skin color, 282-285 in Jamaica, 417 in U. S. 417 MULLER, JOHANNES, 478 MULSOW, 132-135, 499 Multiple factors, in oats and wheat, 281 skin color, 282-285 size, 285-287 Multiple sclerosis, 295 MUSCA, symmetry of egg, 169 Muscular atrophy, 295 Mutation Theory, 305 MUTATIONS, 209-211 AND FLUCTUATIONS, 211, 212, 389 progressive and regressive, 394 origin of, 310-314, 348, 388- 392 Mutilations, not inherited, 339 Myopia, 200 NAGELI, idioplasm, 97 non-inheritance of alpine habit, 345, 495 Natural selection, 377, 380, 402, 438 nullified, 408-411 Nature, definition of, 446 man part of, 447 mechanistic conception of, 446 vs. nurture, 301 stability of, 399 voluntaristic conception of, 444 NECTUHUS, behavior of, 69 Neo-Darwinism, 45 Neo-Lamarckism, 45 NEREIS, spermatozoon of, 17 maturation and fertiliza- tion of, 20, 21 528 INDEX NETTLESHIP, hereditary cata- ract, 198, 199, 499 Neural plate, groove, tube, 28, Neuritis optica, sex-linked, 296 Neuropathy, 295 New England families dying out, 435 NEWTON, 474 Night blindness, sex-linked, 296 NILSSON-EHLE, multiple factors, 281, 282, 499 Notochord, 29 NUCLEAR CORRELATIONS, 162 Nuclear division, indirect, 21, 24, 110, 112, 113, 114, 115, 116, 120, 122, 123, 125, 126 Nuclear inheritance theory, 162- 167 Nucleus, 10, 109, 113 and cytoplasm concerned in heredity, 177, 179 Nulliplex character, 249 Obesity inherited, 203 OBSERVATIONS ON INHERITANCE, 191 "Odd" chromosome, 140 OENOTHERA, mutants, 392, 39S chromosomes of, 392 Oneness of life, 5, 47 Ontogeny and Phylogeny, 7, 302 Oocytes, 129 of rabbit, 130 Oogenesis of Ancyracanthus, 134 Oogonia, 128 Oosperm, 13, 16 double cell, 18 individuality of, 18, 19, 22 infection of, 201 Organ-forming substances, 84 in Styela, Amphioxus, frog, 118, 119 Organism of humanity, 489 Organization, 10 ORGANOGENY, 28 ORIGIN OF SEX CELLS, 126-138 DIVISION PERIOD, 128 Primitive sex cells, 128 Oogonia, 128 Spermatogonia, 128 GROWTH PERIOD, 129 Oocytes, 129 Spermatocytes, 129 MATURATION PERIOD, 135 Orthogenesis, 305 OSBORN, Cartwright Lectures, 398, 499 Otosclerosis, 200, 296 Ovaries, transplanted, 343-3^0 OVIPARITY, 30 Oviparous development, 18, 19 Ovules, 13 Oxychromatin, differential dis- tribution, 184 in cell body, 181 "Pangenes" of deVries, 100 Pangenesis, hypothesis of, 92, 335 PARAMECIUM, avoiding reaction, eg behavior of, 61 reactions to heat and cold, 53 races differing in size, 198 races of, 205 rapid breeding of, 290 selection in, 378 trial and error, 63 Parthenogenesis, 108 "Particulate" inheritance, 208 Partition walls between cells, 185 PASTEUR, 474 PATHOLOGICAL CHARACTERS IN- HERITED, 199-202 PEARL, action of selection, 379, 500 PEARL AND PAHSHLEY, modifica- tion of sex ratio, 149 PEARSON, ancestral inheritance, 216 albinism in European fam- ily, 292 albinism in Papuan family, INDEX 529 inheritance of tuberculosis, 201, 600 statistics, fault of, 221 PEARSON and NETTLESHIP, 289, 292, 500 Permutations in distribution of chromosomes, 156 Personality, determined by her- edity, 449 development of, 7, 77, 460 infinity of chances in, 425, 426 not predetermined, 453 potential, 474 prediction impossible, 424 PHENOMENA OF DEVELOPMENT, 6 Phenotype, 241, 243, 245, 248, 381 vs. genotype, 96 PHYLLOXERA, degeneration of male-producing spermato- zoa, 150 Physiological characters, in- heritance of, 202 division of labor, 37 processes, 10, 12 states, 68, 464 tests, 39, 54 units, 100 Pigeons, behavior of, 70, 71 numerous races, 368, 369, 370 Pineal gland, 163 PITHECANTHROPUS ERECTUS, skull, 397 "Plasomes" of Wiesner, 100 Plasticity of behavior, 71 "Plastidules" of Elsberg and Haeckel, 100 Plastosomes, equal division of, 184 PLATE, ancestors of German Emperor, 217 factors for coat colors of mice, 259 Mendelian inheritance in man, 290-296, 495, 500 PLATO, on transmigration, 40 Polar bodies, 23, 138 Polarity, 167-168 of "Styela egg, 118, 120, 121 Pollen, 13 Polydactylism, 199, 293 Polyhybrid, 244 Population, normally station- ary, 432-434 of Europe, 433 Poultry, selection for egg pro- duction, 379 PREFOH.MATION, 79-81, 161, 452 PREFORMATION AND EPIGENESIS, 93-85 "Preinduction," in Daphnia, 349 Prepotency, 223 PRESENCE AND ABSENCE HY- POTHESIS, 248-250 Primitive sex cells, 128 Principles of good breeding, violation of, 408 Propagation of worst, 409 PROTENOR, sex differentiation in, 142 Protoplasm, 9 Psychical Anlagen, 47 Psychical development, table of, 78 PSYCHOLOGICAL CHARACTERS IN- HERITED, 204-207 PTJNNBTT, 225, 258, 495 "Pure lines," 378 Puritans and Cavaliers disap- pearing, 434 Purity of germ cells, 234, 235, 251 PYTHAGORAS, on transmigration, 4.0 Race amalgamation, 402 extermination, 402 improvement, 6, 487, 488 preservation, 484 Radium, disintegration of atom, 388, 395, 396 influence on spermatozoa, 311 530 INDEX RANA, grafted tadpoles of, 341, S4i Reactions, of germ cells, 43, 49 machine-like, 465 REASON, 59-66 Reception cone, 109, 110 Recessive characters, 228 "extracted," 230 ratio to dominant, 233 Reduction of chromosomes, 136 REFLEXES, 52-56 Regeneration, in eggs and adults, 318, 321 Reproduction, 12, 36 Responses, varied, 68 Responsibility, 443, 445, 459 definition of, 467 of society, 469, 470, 482 varied, 468, 469 Retinal degeneration, 295 RETZIUS, human spermatozoa, 11, 14 Reversible changes not in- herited, 350 Reversion, 209, 223 Rickets, not inherited, 338, 340 Rigidity of behavior, 71 RIGNANO, "Centre - epigenesis" theory, 347, 495 ROMANES, 369, 370, 495 cattle, 374 fowls, 371, 872 swine, 373 ROME, decay of, 485, 486 ROSANOFF, insanity inherited, 206, 500 Rotifers, induction effect of I alcohol, 349 Salamanders, effects of colored soil on, 350 SALEEB\', 495 Savagery, 363, 396, 411 Scholars, prize, 415 SCHULTZE, double frog embryos, 316 Science, duty of, 480 Segregation, apparent lack of, 280-287 fundamental to Mendelism, 279 of Mendelian factors, 234, 235, 251 of substances in cells, 183 SELECTIVE BREEDING, only meth- od of improving race, 404, 405 Spartan method, 404 Self-control, 471, 475, 477, 478 "Self differentiation," 332, 333 Self discovery, 471, 475 SEMON, "Mneme" theory, 347, 348, 495 Sensitive periods, 310 SENSITIVITY', 48 differential, 48, 52 general, 52 of germ cells, 49 Sex, a Mendelian character, 238, 268, 269 influence of food and tem- perature, 303 Sex cells, fundamentally alike, 13 SEX DETERMINATION, 138-150 in human embryo, 139 in man, 145, 146, 147 McCLUNG on, 141 WILSON on, 141 STEVENS on, 141 Sex glands, effects on develop- ment, 329-331 SEX-LIMITED INHERITANCE, 209y 268, 270, 274 SEX-LINKED INHERITANCE, 209, 270-278, 296 Sex ratio, modification of, 140, 148-150 Sexual reproduction, value of, 157, 416 SHAW, BERNARD, 437 Sheep, cleavage of egg, 23 SHTJLL, heterozygosis, 384 500 INDEX 531 Significance of cleavage, 122, 123, 126 of mitosis, 122, 123, 126 Simplex character, 249 Skin color, 197, 289, 291, 292 mulatto, 282-285 influence of light on, 303 Slow breeding of man, 290, 438 SOBOTTA, fertilization of mouse, 114 Social inheritance vs. germinal, 360-363 Social institutions, deal only with environment, 360 Society, highest grade of or- ganization, 482 power of, 410 responsibility of, 482 supreme duty of, 487, 488, 491 Soil, poor, induction effect on plants, 349 SOMATIC DISCONTINUITY, 92, 97 Somatoplasm, in cell body, 125 Somites, 27, 29 SPARTA, destruction of unfit, 404 Special senses, origin of, 52 Specialized types, 413, 415 SPECIFICITY OF GERM CELLS, 151- 161 SPENCER, physiological units, 100, 495 Sperm centrosome, 16 Sperm nucleus, 16, 24 Spermatocytes, 129 Spermatogenesis of Ancyracan- thus, 182 Spermatogonia, 128 Spermatozoon, 15, 17 formation of, 138 Spina bifida, 325 Spinal cord, development, 28 Spindle, mitotic, 110, 111 Spireme, 111 SPIRILLA, reactions to chemicals, 51 i "Sports," 210 STANDFUSS, mutations of insects, 348 1 Star-fish, isolated cleavage cells, 314 Statistical methods, strength and weakness of, 219, 221 STATISTICAL STUDY OF INHERI- TANCE, 214-223 Stature, inheritance of, 196, 218, 219, 220 tendency to mediocrity, 218, 220 influence of food on, 303 STENTOR, modifiable behavior, 68 Sterile insects, 440 Sterility, 409, 435, 439 Sterilization, 419, 421, 422, 439 STEVENS, on sex determination, 141, 143, 166, 500 Stimuli, chemical and physical, 467 conflicting, 68, 464 definition, 308 DEVELOPMENTAL, 307, 310 chemical, 308 non-specific, 309 physical, 308 external and internal, 67, 457, 464, 465 range of, 468 rational, social ethical, 467 summation of, 57 STOCKAHD, alcohol on spermato- zoa, 311, SIS, 500 experimental cyclopia, 153, 325 Structures and functions, recip- rocal relations, 38, 45 STYELA, anterior half-embry- os, 319 dislocated organs, 322 egg substances, 117-119 gastrulation and larva, 124 half and three-quarter em- bryos, 317- 532 INDEX maturation, fertilization and cleavage, 119, 120, 121 posterior half-embryos, 320 Summation of Stimuli, 57 SUMNER, effect of cold on mice, 349, 500 Superman, 412, 439 SWEDEN, extinct noble families, 436 Swine, wild and domestic, 373 SYMMETRY, 168-170 Synapsis, 131 Syndactylism, 199, 293 Tadpoles, fed on thyroid, thy- mus, adrenal, 326 Talents, unused, 471 parable of, 473 Temperament, inheritance of, 205, 291 Temperature, influence on mu- tation, 310 influence on cell division, 311 TENEBRIO, sex differentiation in, 143 TENNENT, modified dominance in echinoderm hybrids, 267, 500 Teratological characters inheri- ted, 199 TERTULLIAN, 41 Tetrads, 135 THOMPSON, cross of yellow X green peas, 229 diagram of Gallon's 1st Law, 216, 495 Thomsen's disease, 295 THORNDIKE, behavior of dogs, cats, monkeys, 64, 495 "Thoroughbreds," 415 Thymus gland, fed to tadpoles, 326 Thyroid, effects on development, 331 gland, fed to tadpoles, 326 Totipotence, of cleavage cells, 316, 318, 332 TOWER, action of selection, 379 mutations in Leptinotarsa, 310, 311, 348, 391 \ Traducianism, 41 Training of animals, 69 Transmission hypothesis, 91, 92 Treasury of Human Inheri- tance, 294, 495 Trial and Error, 63 Trihybrid, 243, 244, ^5/381 Triplets, hereditary, 204 Trophic correlations, 329 TROPISMS, 52-56 TSCHERMAK, rediscovery of "Mendel's Law," 224 Tuberculosis, inheritance of, 201, 202 Turbellarian type of egg, 178 Twins, fraternal, 324 hereditary, 204 identical, 213, 323, 358, 457 Ultra-microscopic units, 100 Uniqueness of every individual, 155, 212, 213 UNIT CHARACTERS, 250, 252, 253 UNITS OF LIVING MATTER, 97-102 ultra microscopic, 100 units of growth and di- vision, 98, 99 units of heredity, 99-102 Unity of organism, 46 Universal laws, 451 Use and disuse, effects of, 329 effects not inherited, 339 Uterus, attachment of oosperm to, 31 Variability, caused by environ- ment, 388 Variations, continuous, 210 discontinuous, 210 fluctuations, 211, 212 meristic, 210 mutations, 211, 212 "sports," 210 INDEX 533 Varied responses, 68 Vegetative pole of egg, 167, 168 VlVIPARITY, 30 Viviparous development, 18, 19 WALTER, diagram of Galtonian inheritance, 208 filial regression, 220, 495 Wars, effects of, 422, 423 shake off social heredity, 363 Wasserman test, 154 WATASE, symmetry of egg of Loligo, 169 WEEKS, 206, 501 Weidal test, 154 WEISMANN, determinants and biophores, 100, 255 germ plasm theory, 96, 100, 335 hereditary and environ- mental variations, 212 on differential division of chromosomes, 125 inheritance of acquired characters, 335 nuclear control of differ- , entiation, 181 reduction of chromosomes, 137, 496 WHITMAN, behavior of clepsine, 68 Necturus, 69 pigeons, 70, 71 freedom and choice, 71, 72, ! 501 WHITNEY, induction effects ofi alcohol, 349, 501 WIESNER, plasomes, 100, 501 WILDER, duplicate twins afcd double monsters, 323, 501 WILL, 67, 72, 459 absolutely free, 445 denned, 470 good and evil, 445 inherited, 205 nature, expression of, 444 supreme faculty, 471 training of, 470, 471 WILSON, distribution of factors, 262 of chromosomes, 263 dwarf and double Amphi- oxus embryos, 315 on sex determination, 141, 142, 144, 166, 167, 496, 501 WINIWARTEH, on chromosomes of man, 145-^6 oocytes of rabbit, 130, 501 WOLFF, "Theoria Generationis," 82, 501 WOLTERECK, induction effects of cold, 349 preinduction, 349, 501 Women's Colleges, influence on marriage, 430, 431 WOODS, "Heredity in Royalty," X-rays, influence on spermato- zoa, 311 X and Y chromosomes, 143, 166 Yolk, influence on size of egg, 13, 14 Zygote, 13 I Ml II I 'I III ' I 1 ! L 006 867 932 3 UC SOUTHERN REGIONAL LIBRARY FACILITY AA 000725176 2