Transome

“ In one sex they are fully developed, in the other rudimentary or wanting. But the sex, usually the female, in which they are rudimentary or wanting is capable of transmitting them to offspring, and also is capable of developing them more or less completely when the ovaries are removed, atrophied or diseased. If we state these facts in the terms of our present conceptions of chromosomes and determinants or factors, we must say that the factors for these characters are present in the chromosomes of both male and female gametes. ”

“ As soon as some of the cells derived from the primary protoplasm of the ovum have developed themselves into genital cells, the other elements which have originated from the same ovum are in such a manner conditioned that, in the latter stages of their vitality, they adapt themselves, and, in short, adapt the properties inherent in all the cells, to the sex of the individual. According, as the ovum is male or female, so are also the cells which originate from it either all male or all female. ”

“ Leaving out of consideration the question of reproduction in lower types of animals we may consider the nature and origin of these cells in highest vertebrates, such as the mammals, including man. Germ-cells, which are derived from the tissues of a female animal, are termed “ova.” Those which are derived from the tissues of a male animal are termed “sperms.” Notice that it is not these germ-cells themselves to which the terms male and female, indicative of the two sexes, are applied, but only to the individuals. They are male and female; the germ-cells are of neither sex. ”

“ As has already been said, this use of the sex organs, merely to produce progeny, and so insure a continuance of the race, is a quality that mankind shares with all the rest of the animal kingdom. In all essentials, so far as the material parts of the act are concerned, the beginnings of the new life in the human family differ not a whit from that of any other mammals. In each case the ovum is produced by the ovaries of the female, passes into the womb, is there met by the semen from the male, fertilized by the spermatozoa, and so the foetus gets its start. ”

“ Transmissionists contend that somatic modification in a given direction in one generation is transmitted to the reproductive cells to constitute a source of germinal variation in the same direction in the next generation. ”

“ In consequence there are two classes of sperms in man; female producing containing 24 chromosomes, and male producing containing 23 chromosomes. If the factor for color blindness is carried by the X chromosome its inheritance in man works out on the same chromosome scheme and in the same way as does white eye color (or any other sex linked character) in the fly, for the O sperm in man is equivalent to the Y sperm in the fly. ”

“ Both the X and the Y sperm have been shown to produce the sex opposite to that which they normally produce when they fertilize eggs that are normal in every respect, except that of their X chromosome content. These facts establish experimentally that sex is determined by the combinations of the X chromosomes, and that the male and female combinations are the causes of sex differentiation and are not simply the results of maleness and femaleness already determined by some other agent. ”

“ A living being takes its individual origin only where there is separated from the stock of the parent a little piece of the peculiar reproductive plasm, the so-called germplasm. In sexless reproduction one parent is enough; in sexual reproduction equal masses of germplasm from each parent combine to form the new individual. The germplasm resides in the nucleus of cells, and Weismann identifies it with the nuclear material which microscopists have named chromatin, on account of the avidity with which it absorbs certain dyes. ”

“ In man and in domesticated animals we find that individuals appear occasionally that are defective in one or another respect. Some of the defects are inherited. Rarely a new one appears that has not been seen before. But the majority of them are reappearances of characters that have been carried under the surface as recessive genes in the germ-plasm. Today we recognize that each of these modifications, if recessive, has first arisen as a mutational change in a single gene before it appeared on the surface as a character by the coming together of two such genes. ”

“ Here—since it is obviously impossible for all the cells of one individual to fuse with all the cells of another—certain special cells are set apart in each organism for the purpose of union or conjugation; and it seems quite natural that in the course of time the differentiation spoken of above, into male and female, should set in—each individual tending to become decisively either masculine or feminine—both in the sex-cells or sex-apparatus, and (though in a less marked degree) in the general ‘body’ and structure. ”

“ The normal sexual act has been described as consisting in the fusion, first, of two cells, then of their nuclei, and finally, often after a long interval, of their chromosomes and of their chromomeres in meiosis. What causes determined these fusions is a question that is only partly answered. It is known in certain cases (e.g. ferns and mosses) that the male cell is attracted to the female by chemical substances secreted for the purpose by the female organ ”

“ Since in a normal male, however, the mature reproductive cells will contain either a normal X or no X (fourth row) , any one of four different kinds of matings may result. A sex-cell carrying normal X of the male may combine with an ovum containing normal X producing a normal female (row five) . Or such a cell may combine with an ovum carrying the defective X, also producing a female but one who although of normal color vision herself, like her mother, is a carrier of the defect. ”

“ Now in these simple products of nature, if the female contributed to produce the new embryon equally with the male, there would probably have been some visible similarity of parts for this purpose, besides those necessary for the nidus and sustenance of the new progeny. Besides in many flowers the males are more numerous than the females, or than the separate uterine cells in their germs, which would shew, that the office of the male was at least as important as that of the female ”

“ For if brain substance, for example, contributes nothing to the reproductive cells, any modification it acquires during individual life can only reach the germ through some indirect mode of influence. But does it-does any modification of the body substance -- so affect the germ as to become hereditary? Prof. Weismann answers this question by asserting that the evidence for the direct transmission of acquired characters is wholly insufficient, and by contending that, until· satisfactory evidence is forthcoming, we may not accept transmission as a factor in evolution. ”

“ There the double cell, so formed, develops into the new individual. But in higher forms the meeting takes place, and the first stages of development ensue, within one of the bodies. And, as one might expect, this occurs within the body of the female. For the female, as we have said, represents quiescence, growth, assimilation. The germ or ovum is large compared with the spermatozoon; it is also sessile in habit. The spermatozoon, on the other hand, is exceedingly active. And so it seems natural that the latter should seek out the germ within the body of the female. ”

“ The illustrious author of the Germ-Plasm has made it quite clear that there is a great difference between admitting that the germ-plasm has no charmed life, insulated from bodily influences, and admitting the transmissibility of a particular acquired character, even in the faintest degree. The whole point is this: Does a change in the body, induced by use or disuse or by a change in surroundings, influence the germ-plasm in such a specific or representative way that the offspring will exhibit the same modification which the parent acquired, or even a tendency towards it? ”

“ Therefore we have made use of a trick we call “marking the chromosome,” which means that we use a male whose sex chromosome carries a known gene near the tumor locus. By using this type of male in successive generations we get two types of daughters: one type like their surviving brothers in eye color that do not carry the tumor-gene and the other daughter with normal eyes that carries it. ”

“ If we accept the idea that characters are represented by particular parts of the chromosomes, according to Morgan's scheme, our theory of development is the modern form of the theory of preformation. When in the course of development the cells of the head from which the antlers arise are formed, each of these cells must be supposed to contain the same chromosomes as the original ovum from which the cells have descended by repeated cell-division. ”

“ ESSENTIAL PREMISES The mechanism of heredity lies in a single germ cell carrying the character-determining chromosomes which consist of organized chains of genes. In the character and organization of these genes in the fertilized cell we find the complete "blueprint" for the future individual in so far as it is to be determined by heredity. In the twenty-four pairs of chromosomes in the fertilized human germ cell we find the long and diversified heritage of each parent represented through the union of the sperm and the ovum. ”

“ Cytology is in fact a branch of anatomy, and in the anatomy of the cell we have made some progress, but our knowledge of the physiology of the cell is still infinitesimal. The nucleus, and especially the chromosomes, are supposed in some unknown way to influence or govern the metabolism of the cytoplasm. From this point of view the hypothesis mentioned above that the sex-difference in the gametes is not qualitative but quantitative is probably nearer to the truth. ”

“ But it is a living nutri ment, in some respects comparable to that which would be supplied to an animal kept alive by transfusion, and its molecules transfer to the impregnated embryo cell all the special characters of the organism to which it belonged.
The tendency of the germ to reproduce the characters of its immediate parents, combined, in the case of sexual generation, with the tendency to reproduce the characters of the male, is the source of the singular phenomena of hereditary transmission. No structural modification is so. ”

“ It has become a familiar statement that every individual is the result of its heredity and its environment. The thesis that I desire to establish is that the heredity of each individual and each type is compounded of variations or changes of two distinct origins, one external and one internal; that is to say, of variations resulting from changes originating in the germ-cells or gametes, and of modifications produced originally in the soma by the action of external stimuli, and subsequently affecting the gametes. ”

“ In a crisis, when the life of one of the two seeds is trembling in the balance, one of them—through the exertion of its "Latent Reserve Energy," dominates, and engenders a child of the opposite sex. This reversal of the sex is in conformity with the Law of the Cross-Transmission of Sex; that is, the mother is represented in the male offspring and the father in the female,—this being the normal expression of the Law of Cross-Transmission of Characteristics. ”

“ The blood corpuscles of man and woman are the same, and so are the cells of their nerves and muscles; and even the sexual cells, so different in size, appearance, and generally also in motile power, must contain the same fundamental substance, the same idioplasm. Otherwise the female germ-cell could not transmit the male characters of the ancestors of the female quite as readily as the female characters, nor could the male germ-cell transmit the female quite as readily as the male characters of the ancestors of the male. ”

“ In countless experiments it is shown that the transformed female becomes like the male of her own strain and brood—to state it simply, like the male she would have been if she had not been a female. If we think of this basis as single, then it must exhibit itself in one way in the presence of the male secretions, in another way under the influence of the female secretions. In this way a very simple chemical agent in the secretion might account for the whole difference—merely causing a genetic basis already present to express itself in the one or the other manner. ”

“ Cells attract each other just as human beings do; and the attraction seems to depend, to a certain degree, on difference. The male spermatozoon seeks the female ovum, just as the male animal, as a rule, seeks and pursues the female. Primitive cells divide and redivide and differentiate themselves, building up the animal body, just in the same way as primitive thoughts and emotions divide and redivide and differentiate themselves, building up the human mind. ”

“ Some authorities think that "every cell in the body is an organ of internal secretion", [2] and that thus each influences all the others. The sex glands are especially important as endocrine organs; in fact the somatic cells are organized around the germ cells, as pointed out above. Hence the sex glands may be considered as the keys or central factors in the two chemical systems, the male and the female type. ”