Spermatozoon

“ The human spermatozoon measures about one six-hundredth of an inch in length. It is composed of protoplasm, the substance of which all living creatures are composed. The spermatozoa are believed to be developed from a parent sperm-cell, by the process of segmentation or subdivision, which process is common to all cell-life. The numerous spermatozoa dwell in a gelatinous substance, which, mingling with the other fluidic secretions of the glands of the male, constitutes the male seminal fluid, sperm, or semen, which is ejaculated by the male during the process of copulation. ”

“ On the other hand, there is considerable evidence that the ovum has some share in the effect, and if this is so, before any practical results are reached it will be necessary to discover which of two conceivable causes of sex-determination is the true one. It is possible that there are two kinds of ova, as well as two kinds of spermatozoa, and that there is a selective fertilization of such a kind that one kind of spermatozoon only fertilizes one kind of ovum, the second kind of spermatozoon the second kind of ovum. ”

“ In normal fertilization, as a rule, only one spermatozoon fuses with the ovum. It has been observed in some eggs that a membrane, formed round the ovum immediately after the entrance of the spermatozoon, prevents the entrance of others. If Gametogeny. than one spermatozoon enters, a corresponding number of male pronuclei are formed, and the subsequent development, if it takes place at all, is abnormal and soon ceases. An egg by ill-treatment (influence of chloroform, carbonic acid, &c.) can be made to take more than one spermatozoon. ”

“ But the spermatozoon-form of male cell does not occur only in animals and plants which live in the water, or in those which, like mosses and many vascular plants, are at least occasionally covered by a thin layer of rain or dew, in which the zoosperms can swim to the ova, it occurs also in a very large number of animals in which the sperms pass directly into the body of the female, in those, therefore, in which copulation takes place. ”

“ In the history of the male element or spermatozoon, there is an analogous reduction, so that when spermatozoon and ovum unite in fertilisation the normal number is restored. It is now recognised that the maturation-divisions are useful in obviating the doubling of the number of chromosomes which fertilisation would otherwise involve, and it has also been suggested that this continually recurrent elimination of chromosomes may be one of the causes of variation. ”

“ Returning to the ovum which meets a spermatozoon in the course of its journey down the tube, we find that as soon as a spermatozoon enters an ovum it disappears and is completely absorbed, and, as the ovum in turn is instantly possessed of new powers, through the presence of the male cell, the result of this union is an entirely new cell. ”

“ But nature is lavish where the propagation of the species is concerned. A portion of an ovary or of both ovaries might become diseased, and thousands of ova might become unfit for fertilization; nature therefore puts in an extra reserve supply. We see a still more striking example of this extreme extravagant lavishness in man; only one spermatozoön is necessary to impregnate the ovum, and only one spermatozoön can penetrate the ovum; nevertheless each normal ejaculation of semen contains between a quarter and half a million spermatozoa. ”

“ Many of the spermatozoa, weaker than the others, perish on the way, and only a few continue the journey up through the uterus to the tube. When near the little ovum, which remains passive, their movements become more and more rapid, they seem to be attracted to it as if by a magnet, and finally one spermatozoön—just one—the one that happens to be the strongest or the nearest, makes a mad rush at it with its head, perforates it, and is completely swallowed up by it. ”

“ That of the male is called the spermatozoon (pronounced sper ́ma-to-zoön) . It is sometimes called spermatozoid; the plural is spermatozoa. It is exceedingly small, the smallest of any cell in the body, and has the power to move from place to place. These cells are produced in enormous numbers, and so far as they have been observed under the microscope they differ considerably in power of movement and in perfection of development. Considering their small size, they must make a [163] very long journey to find the ovum; and if they were only few in number, they would rarely succeed ”

“ Since only one spermatozoon enters the ovum, whether or not the child will be a boy or a girl depends entirely upon which type gains entrance. If this explanation is correct, and it is in accord with careful biological observations, it removes from the mother all responsibility for the sex of her child. Furthermore, since the facts indicate that male-producing and female-producing spermatozoa are present in equal numbers, it follows that practically there is an even chance that an embryo will develop into a boy or a girl. ”

“ In most cases which have been investigated the divisions by which the spermatids arise from the spermatocytes are two in number, so that each spermatocyte gives origin to four spermatids. Each spermatid becomes a functional spermatozoon or male gamete. The gametogeny of the male therefore closely resembles that of the female, differing from it only in the fact that all the four products of the progamete become functional gametes, whereas in the female only one, the ovum, becomes functional, the other three (polar bodies) being abortive. ”

“ The spermatozoon is one of the smallest of known cells, frequently being no more than one hundred thousandth of the size of the ovum, although the extraordinary case of a small Cypris has been recorded in which the spermatozoa are longer than the animal. It is produced in enormous quantities and relatively to other minute cells is extremely tenacious of life. It may retain its vitality in the male organism for a long time after it has become a separate cell, and may exist for lengthy periods in the female organism. ”

“ Spermatozoa originate in the testis as cells, which are filled with granules. After a time, each granule acquires a long appendage, and then the cell has become converted into a bundle of small zoösperms. Development still continues, until finally the thin pellicle on the outside of the bundle is ruptured, thus liberating the young spermatozoa, which speedily complete their full development. The spermatozoön is pure protoplasm, which is the basis of all life, and its power of spontaneous motion is due to this fact. ”

“ Boveri, who has further extended our knowledge of the process, considers that the spermatozoon removes an inhibitory influence preventing the commencement of development in the ovum; the spermatozoon replaces a portion of the ovum which has already undergone degeneration, so that the object of conjugation is chiefly to effect the union of the properties of two cells in one, sexual fertilization achieving a division of labor with reciprocal inhibition ”

“ From time to time, they back out of such a cove and seek another mooring place.
“This ‘stationary hunting’ motion is less universal than the other two. Many individual spermatozoa fail to attain it. It seems probable that only the most vigorous individuals ever reach this stair”. It has not been encountered in unmixed semen or in any artificial mediums. It has been observed only when the spermatozoon is in the secretions of the female genital tract. It is 21most frequent when the spermatozoon is in contact with a nest of epithelial cells.... ”

“ Fecundation results and conception ensues, the ovum then remaining attached to the walls of the Uterus, and in time develops into the foetus. If, however, the ovum is not impregnated, because of absence of copulation or from other causes, it gradually loses its vitality, and is finally cast off with the several uterine secretions.
It should be explained here that the "spermatozoon" of the male (the plural of the term is "spermatozoa") is the male generative "seed." The sperum, semen, or seminal fluid of the male is filled with hundreds of thousands {29}of spermatozoa. ”

“ But the developmental processes which lead to the formation of fully developed ova and spermatozoa come to a full stop before fertilization and they do not usually begin again until a spermatozoon has entered an ovum, or until the latter has been stimulated by some other outside means. In some animals and plants eggs may develop regularly without fertilization, the stimulus to development being supplied by ”

“ On the occasion of the next nocturnal emission the ampullæ will empty along with the seminal vesicles and these spermatozoa pass out. If they be examined under the microscope as a part of a normal nocturnal emission, they will be found to be almost motionless or very greatly lacking in typical spermatozoon activity. ”

“ The ovum may remain for a period, and the spermatozoa that seek the ovum may enter, but neither may tarry unless each yields itself to the other in that mysterious union which results in life. Apart or alone, after a brief period, they must alike be cast out; no idler may tarry there; but that semblance to innate intelligence which rejects or casts out any incomplete part as a foreign substance accords a hearty welcome to the ovum that has been quickened into a new life by the entrance of a spermatozoön. ”

“ Seen under a microscope, a single drop of semen reveals a multitude of spermatozoa swimming about in the prostate-carrying medium. It is in this form that the vitalizing male element meets the female infertile ovum. This mass of live and moving germs is poured all around and about the region in which the ovum lies waiting to be fertilized, and every one of them seems to be "rushing about like mad" to find what it is sent to do, namely, to meet and fertilize the ovum. ”

“ There does not appear to be any true copulation. The male deposits small, white, oval spermatophores, which consist of small bundles of spermatozoa cemented together by some glutinous substance, indiscriminately on any part of the body of the female. Such spermatophores are found on the bodies of both males and females from July to January, but they appear to be most numerous in our autumn. It seems probable that the spermatozoa make their way from the adherent spermatophore through the body wall into the body, and so by traversing the tissues reach the ovary. ”

“ Now fertilisation does not necessarily occur whenever the male organ comes in contact with the female organ. Fertilisation occurs only when a male-cell (spermatazoon) unites with a female-cell (ovum) ; in other words, when the spermatazoa in the seminal fluid of a man meet and unite with the germ or ovum in the body of a woman. That is the beginning of the child. This union of the two cells need not take place during or immediately after sexual intercourse. It may occur many hours, or even two or three weeks, after connection, because the spermatazoa have motion of their own. ”

“ It is incorrect to suppose, as has been held by some{121} theorists, that one testicle give rise to male spermatozoa and the other to female spermatozoa, for both male and female offspring have been produced from the same male parent after one testicle or the other has been removed. The same is true in cases in which either ovary has been removed from the mother; that is, male and female offspring are produced from mothers in whom either ovary has been removed. ”

“ It is much easier to understand why abnormal spermatozoa occur so frequently, or changes take place in the semen with death or weakening of the germinal elements, if we realize or stop to consider the highly differential process of spermatogenesis, and the various structures which contribute to the formation of the semen. We must come to realize that each part of the genital tract is essential to the normal functioning of the whole, and that the genital tract and reproduction are in turn dependent upon the proper functioning of the entire body. ”

“ The semen, made up as it is of mixed products of the testes and accessory sexual glands, is very often abnormal, as would be expected in view of the frequency with which changes occur in the glands contributing to its formation. The normal semen is remarkably adapted to its function of nourishment and stimulation of the spermatozoa, and their conveyance to the internal female genital organs. The spermatozoa are extremely sensitive to changes in their environment, with the result that any alteration of the physical or biochemical content of the seminal fluid may cause death of the sperms. ”

“ The Spermatozoan is structurally much different from the ovum, but it also has its nucleus and chromosomes, which carry to the child the transmittable characteristics of the father.
The ovum is usually comparatively large and stationary, and whatever motion is therefore necessary to bring it into contact with the male cell devolves upon the latter, which possesses what is known as a locomotor tail. In addition there are usually many sperms to one ovum, so that the chances are that at least one male cell will reach the egg and effect fertilization, and the beginning of a new life. ”

“ In the male the testis is a specialized portion of the wall of the genital coelom, and has a structure comparable to that of the ovary. The spermatozoa pass through an orifice from the cavity of the testis to the genital capsule, and thence to the spermiduct. The spermiduct is provided with a glandular pouch, and opens into a terminal reservoir known as Needham’s sac or the spermatophore sac. The function of this pouch is to form the spermatophore, which is an elastic tube formed of structureless secretion and invaginated into itself. ”