Chapter 2 - The Mechanics Of Reproduction

It might seem that what occurs when two unisexual mammals copulate is too well known to require restatement in a book for adults, especially for adults who are actual or potential breeders of dogs or other domestic livestock. The outward aspects of the sexual act are fairly well known and, even if they were not known, would be of but little consequence. But there is an incomprehensible lack of information on the part of the public about the fundamental reproductive processes: the basic and functional sex cells, their origin, their structure, how they unite and how the new organism develops. Even that part of the public whose particular business it is to utilize such knowledge in the breeding of animals is all too often deficient in such information.

Mere egotism, the circumstance that we are ourselves unisexual mammals, curiosity about how our own species reproduces itself, would seem to be a stimulus which should prompt us as humans to want to know the fundamental facts about the sexual mechanism. But for a very large part of the population mere curiosity has not been great enough to justify the intellectual effort.

Many lower organisms reproduce themselves without resort to sex. In others, somewhat higher in the biological scale, both sexes exist in one organism. While the evolution of the reproductive process is an interesting theme, its consideration is not essential to our subject and would prolong this text beyond practicable limits. We must confine our discussion of the subject to the reproductive processes of the dog. Any mention of other species is made only insofar as it is analogous to or illuminative of the breeding of dogs.

The canine species, of which the domestic dog (Canes familiars) is a part, is a placental mammal. Like all such higher mammals it is divided into two sexes: females (bitches) and males (dogs). The term dog may be correctly applied to a member of either sex. The primary differences between the two sexes lie in their reproductive apparatus and the part each plays in the reproductive process.

Both dogs and bitches are normally equipped with glands of reproduction, known as gonads, from which issue the cells which unite to form the new organism. The two gonads of the female are known as the ovaries and in them the ova (singular, ovum), or eggs, have their origin. The gonads of the male dog are known as the testes (singular, testis), or testicles, and produce the spermatozoa (singular, spermatozoon), or sperm cells, which unite with the ova, thereby fertilizing them. The spermatozoa carry in themselves the determining contribution of the male to the new organism. The ova and spermatozoa are known collectively as gametes.

The gonads serve other purposes than merely to develop and discharge the reproductive cells. They are also ductless glands of internal secretion and their hormones have much to do with the character and appearance of their host. The corpus luteum function of the ovaries and its effect upon the development of the embryo are discussed later in this chapter.

The resultant sex of the new organism is determined at the very moment of the fusion of the sperm and the ovum. The mechanics of this phenomenon, which is conception, will be treated in the chapter "Determination of Sex." It is sufficient here to say that it is true.

From the fusion of the parental gametes, from the single fertilized egg, will develop the entire organism destined to be a newborn puppy. By the division and proliferation of the cells there will come into being bones, muscles, and tissues, to form that complex animal, a dog. By the fourth week of embryonic development some cells are specialized and set aside, ultimately to act as reproductive cells to enable the dog to reproduce its kind. These basic reproductive cells form but a small fraction of one percent of the dog. As such, they serve the individual in no way. They play no direct part in his metabolism or body chemistry. The dog is merely their host and carrier. They are the stuff of future generations. The other cells of the body nourish and care for them, but they contribute nothing in return. Their duty is to the species, not at all to the individual animal.

In the male the reproductive material is housed in the testes and develops into spermatozoa; in the female it is in the ovaries and develops into ova. New life in the higher animals arises only from the union of a spermatozoon and an ovum.

The ovaries are the organs which house the germ plasma of the female and which produce the egg or ovum. In addition to the reproductive cells the ovaries also contain the interstitial cells which have other functions not primarily concerned with the reproductive process. The female is born with all of the ova (in an undeveloped and unripened state) that she will ever produce. Each ovum lies in a Graafian follicle, a tiny spherical vesicle which nourishes the developing egg. In the sexually mature bitch the ova in various stages of growth are scattered about in the ovary. The Graafian follicle is originally a simple layer of cells, but as the ovum ripens the follicle thickens and becomes more complex in structure.

When the ovum is fully ripe the Graafian follicle bursts, discharging the ovum. The empty follicle now becomes the corpus luteum, "yellow body," ready to regulate several of the processes of pregnancy. In effect, the corpus luteum is a gland of internal secretion, producing hormones to counteract other hormones which would bring about menstruation and expel the fetus prematurely. The hormones of the corpus luteum also stimulate the milk production in the mammary glands. (It is from the presence of these special milk-producing glands that the entire biological class derives its name MAMMALIA.) The corpus luteum, by the exhaustion of its hormones, determines the time of birth of the new organism.

Having burst from their follicles, the ripe ova pass into the oviducts, or Fallopian tubes, which lead, one from each of the two ovaries, to the uterus. The ovarian end of the oviduct is larger than the tube itself and partly surrounds the ovary. In the dog, but not in man, the ends of the oviducts surround the ovaries with a membrane in such a fashion that it is impossible for the ova to escape into the bitch's abdominal cavity where they might possibly be fertilized by the persistent sperm. In this respect, at least, the dog is more complexly evolved than Man, for in Homo sapiens the female lacks such an enclosing membrane and an extra-uterine pregnancy is possible.

It is in the Fallopian tube that the ripe ova normally encounter the sperm cells and are fertilized, provided of course that the bitch has been mated, that the sperm mass is sufficiently large, and that the sperm are motile and functional. Of the many millions of sperm released by the male at a single copulation, only a small percentage reach the oviduct and, even of them, only as many can be utilized as there are ova to be fertilized. The rest of them will die as a result of chemical changes brought on by the fertilization.

The ripe and unfertilized ova will survive in the oviducts for some seventy-two hours awaiting their fusion with the sperm. If fertilization does not occur, the ova die and are discharged from the body in the next menstrual flow. Once fertilized the growing mass moves from the oviduct into the uterus where it attaches itself to the wall. The fertilized ovum will then continue its proliferation to form all of the new organism.

The vagina is the canal which connects the uterus with the external orifice of the female genitalia in the vulva, the small, muscular organ visible between the rear legs of the bitch. Into this canal the semen is ejaculated by the male dog and passes upward through the cervix and the uterus into the oviduct to seek and fertilize the ova. It is through this canal that the resultant puppies are born into this breathing world.

That the urethra, the urinary outlet from the bladder, empties itself at the exterior end of the vaginal canal, is not a matter for extended comment.

The uterus, or womb, is situated in the ventral posterior part of the abdominal cavity. When the bitch is not pregnant, or "in whelp," the uterus is small, only some three inches long in the larger varieties of dogs, and proportionately smaller in smaller breeds. The uterus has two "horns," or branches, the end of each of which connects with one of the oviducts. As pregnancy progresses, the uterus stretches and enlarges to accommodate the developing embryos. When the pregnancy terminates and the embryos are expelled, the uterus will contract to its smaller, non-pregnant size.

Only the briefest mention need be made of the clitoris in the bitch since this small organ plays no part in the reproductive process. Located just above the vaginal opening, the clitoris is the counterpart in the female of the male penis. In the human female its stimulation will ordinarily induce orgasm, though in the dog its purpose is not so clear-cut. There is very little evidence relating to the orgasm in lower forms.

It should also be noted that the virgin bitch has no hymen or maidenhead.

In the male dog the testes, or testicles, are normally two in number. Roughly egg-shaped, they hang suspended from the body between the hind legs in a sack of skin, the scrotum. (Cryptorchidism, the retention of the testicles in the abdominal cavity, will be dealt with in the chapter, "Sterility, Impotence, and Cryptorchidism.") It is in the testicles that the spermatozoa are developed from the basic sex cells.

A testicle is fundamentally a structured mass of tubular tissue, the lining of which is constantly throwing off new cells. Some of these new cells will become functional spermatozoa while others will produce only additional sperm-forming cells.

Basically, each testicle is actually two glands: one for the production of functional sperm; the other a male endocrine gland manufacturing needed hormones which are only incidentally a part of the reproductive process. A single, normal testicle in a healthy dog will produce enough useable sperm to repopu-late the entire canine world and the fact that each normal dog has two such organs is merely nature's "margin for safety."

Within the testicle is the epididymis, another tube, very small, many feet long, but tightly coiled. The ripe spermatozoa enter the epididymis and remain there until required, when they are forced out by muscular contraction into the vas deferens. The vas deferens, another spermatic duct, carries the sperm to the base of the penis where they are bathed and further activated by secretions from the prostate and other glands. So bathed and mixed, the sperm are now a single component in the seminal fluid or semen (seed). In the dog no seminal vesicles are present and the sperm are discharged directly from the vas deferens into the urethral canal of the penis and from there into the vaginal canal of the bitch. Also absent in the dog are Cowper's glands, the secretion from which in so many animals dilutes the seminal fluid.

The absence of the seminal vesicles and of Cowper's glands makes it necessary for the dog to have prolonged copulation to enable it to discharge its full complement of semen. Instead of a gush of semen from the seminal vesicles, as occurs in organisms equipped with such reservoirs, the orgasm of the dog must be a slow trickle which may require from several minutes up to half an hour or longer.

The characteristic method of coitus in the dog is made both possible and necessary by the peculiar structure of the penis and by the grasping muscles [Sphincter cunni) of the bitch's vagina. The penis consists of two erectile parts, in the anterior of which there is a bone. The posterior portion, the corpus cavernosum, is much larger and, grasped spasmodically by the bitch's vaginal sphincter, it facilitates the prolonged copulation, during which the male dog may and usually does dismount from the female and stand on all-fours with her, posterior to posterior. Until erection begins to subside, it is impossible for the mating animals to separate one from the other, and forcible separation is liable to injure one or both.

The single spermatozoon is a minute, rounded head, which contains the all-important nucleus of the cell, and a long, whiplash tail by means of which the spermatozoon propels itself in its search for the waiting ovum. Since the over-all length of the spermatozoon is only one five-hundredths of an inch, the lashing tail is "long" only in relation to the extremely small head.

In the head of the spermatozoon is the nucleus of the cell, and in that nucleus is the entire hereditary potential which the male and his ancestors can contribute to the new organism. It has been estimated that a male dog can release between 300 million and 600 million spermatozoa in a single orgasm, each one of which is theoretically capable of fertilizing an ovum. So large a number of sperm seems to imply that nature is over-generous in the production of male procreative material. However, it has been recently learned that there is a significant correlation between sperm-mass and fertilization. When the sperm-mass falls below 150 million the likelihood of fertilization occurring is reduced by almost seventy-five percent. The larger sperm-mass is necessary to the proper acid-alkaline balance of the bitch's genitalia, for if the bitch's uterus or oviducts are too acid or too alkaline the sperm are immobilized and die before they can reach the ova. The size of the sperm-mass acting as a chemical reagent is quite independent of the fact that even in the smaller mass the sperm might be motile and thoroughly functional, i.e., capable of fertilizing the ova. The use of artificial insemination will be discussed later in this book.

The onset of menstruation usually occurs for the first time in the bitch somewhere between her eighth and tenth month of age. There is a fairly wide range of variation with respect to the menarche (the first menstrual period). Menarche tends to vary inversely with the size of the breed, being at an earlier age in the smaller breeds. Even within a single breed there is considerable variation of the time of menarche since the phenomenon is contingent upon adequate or inadequate nutrition, upon environmental factors, and also upon a hereditary element which hastens or retards it with respect to the norm for the given breed.

Menstruation is a cleaning of the walls of the uterus in its preparation to receive the fertilized eggs. Hormones originating in the anterior portion of the pituitary gland, the Graafian follicle, and the corpus lute urn initiate the process. The first indication of menstruation is a swelling of the vulva, which may be noticeable at any time from a few hours to a few days before the onset of menstruation proper and the discharge of the bloody menstrual fluid. This discharge normally continues some eight to ten days, although its duration may be much shorter, seldom longer than that.

Various psychic phenomena, or none, may occur during menstruation. Some bitches seek seclusion, some take to wandering and prowling, some are erratic of appetite.

It is after the cessation of the menstrual flow that the bitch's mating instinct asserts itself. Normally, it is only during the week to ten days, more or less, following menstruation that the bitch is "in heat" and will permit copulation with the dog. Some bitches, especially old and experienced ones, will accept the male before the end of the menstrual flow, whereas, others, usually virgin or young bitches, although menstruation has stopped and the bitches are physiologically ready for breeding, will not accept the dog at all and if they are to be mated they must be held and forced to submit to copulation.

As in most mammalian species, sexual maturity in either sex of the dog is usually attained before complete physical maturity. It is a debatable question as to whether a bitch should be bred at her first heat or before full physical maturity. The answer must depend somewhat on the breed under consideration, somewhat upon the type of the bitch in relation to her breed, and somewhat upon her approximation to physical maturity. It is argued by many breeders that bitches of such breeds as Bulldogs, French Bulldogs, and Boston Terriers, which as breeds are given to difficulties of parturition, should undergo their first pregnancy while the bones of the pelvis are yet flexible, to the end that they may have less difficulty in the whelping of their young, not only in the first but also in subsequent pregnancies.

It is recognized that maternity fills out and matures the higher animals and many bitches of certain breeds may be better specimens of their breeds because of maternal experience. A bitch that lacks skeletal substance, or is too much cut up in the region of the loin, may be improved in either or both those respects by maternity. On the other hand, a bitch of a breed required to have a racy outline may be harmed in her type by being bred and it is better to await the end of the exhibition career of such a one before a matronly figure is permitted to mar her type.

Neither the humane nor the wise breeder will be likely to subject to pregnancy a bitch which falls far short of physical maturity and which requires all her nourishment for the development of her own body without diverting any of it to the development of a litter of puppies and to the suckling of them. However, if the bitch is reasonably healthy and mature, eats well and assimilates her food, to await her full maturity before breeding is probably a waste of time. Genetically, there is absolutely no difference in the viability of the progeny of young bitches and the progeny of older ones. It is a biological law that the developing embryo is parasitic upon the mother and that if there is a problem of insufficient nutrition, the one to suffer will be the mother rather than the embryo.

Some breeders, especially German breeders of German Shepherd dogs, are insistent that bitches should not be bred until full and complete maturity—not before the second, better not before the third, menstruation. In the case of a bitch with an abnormally long back or loin, or one with a tendency to a sway of the spine, or where the food supply is inadequate as it concerns quantity, quality, or balance, this delay is certainly justified; but the using of such a bitch for breeding, or any bitch not properly nourished, at any time is a very dubious experiment. There is, however, much unnecessary loss of time in the awaiting of full physical maturity of normal and well developed dogs before utilizing them for breeding. (The early use of the male dog for breeding will be discussed in Chapter XIV, "Things That Are Not True.")

It is all but needless to say that it is necessary to keep bitches confined during their period of heat, and, indeed, it were best during the entire menstrual and rutting period, unless one choose to take the very probable risk of their being mated promiscuously to such dogs as they may encounter while running at large.

Modesty is not the usual attribute of a bitch in heat and she will use all her ingenuity to escape to find a mate and will usually give her favors to whatever dog or dogs may come her way. The odor of the urine of the bitch in menstruation, or in heat, is an advertisement to dogs of the neighborhood of her condition and it is better not to exercise her where her excretions may serve to attract all and sundry of the neighborhood dogs.

It is possible, and by no means unusual, for a bitch to be bred to two or more dogs during one breeding season, in which case it is frequently impossible to know which is the sire of her litter. Indeed, it is possible that a part of the ova may be fertilized by sperm from one dog and another part of the ova by sperm from another dog. This interesting and not generally recognized phenomenon can occur only when the breedings with the two or more dogs occur without too great an interval between them. The progeny from such mating are not true siblings but are only half-brothers, half-sisters, although it is seldom possible to recognize which puppies are the progeny of which sire.

In cases such as that just mentioned, if the bitch has been bred to only two dogs, both known to be purebred animals of her own variety, some stud books, by special dispensation, will admit the registrations of the progeny with "alternate sires," especially if the dam and both the sires are of such merit as individuals and for their germ plasma s that their progeny is believed to contribute to the improvement of the variety. All of the members of the litter may be sired by one of the dogs, part by one and part by the other, but none can be sired by both. However, for the stud book record, since the actual sire of any puppy is not known, the names of the possible sires must be stated.

Misalliances and such accidents as the ones described are due to a carelessness on the part of the keeper of the bitch, and great care should be used to avoid them.

The bitch does not normally encourage the sexual attentions of the dog between breeding seasons, although coitus when she is not in heat may and sometimes does occur. It is usually a painful experience for the bitch and, since there are no ripe ova, pregnancy does not result. A few bitches are always in heat, probably due to a pathological condition, attracting and accepting the sexual attention of the dog at all times. They are seldom fertile and are nuisances as pets and useless for a breeding kennel.

Occasionally a bitch will menstruate and come into heat at an abnormally short time after her previous normal period of heat. At such "false heats," as they are called, it is believed that there are no ripened ova in the tubes and if she is mated no pregnancy results.

In the normal condition, the fertilization of the ova hastens the subsidence of the heat, which usually lasts but a few days after a successful mating. That, however, is not always true. Whether bred or not, the bitch will gradually go out of heat. This usually requires some eight to ten days during which she attracts the sexual interest of the dog but responds to it at first reluctantly and later not at all.

The favorable time to breed the bitch is as soon after the subsidence of the menstrual discharge as she will readily and willingly accept the breeding service of the dog. This is merely taking time by the forelock. There is no reason to believe, despite old theories to the contrary, that the time of conception determines or influences the sex of the progeny. Early deposited sperm live several days in the uterus and oviducts of the bitch to await the ripening of the ova, just as the ova will live several days awaiting the arrival of the sperm. Early breeding leaves time for other efforts if either the dog or the bitch refuses the advances of the other; and, if the copulation is only doubtfully complete or is in any way unsatisfactory, it permits of a second breeding.

That the parties to the copulation should hang together, as the effect of the grasping of the corpus cavernous by the sphincter cunni, is not an absolute requisite for fertilization. However, if the mated dogs fail so to hang together, there is reason to doubt the success of the mating. The duration of the hanging together is no criterion of the efficiency of the breeding service, very brief copulations yielding as good results as prolonged ones.

While it is only the primary sexual organs, their products and functions, that are here discussed, sight must not be lost of the influence of sex upon the whole organism. Just as surgical removal of the gonads (castration) will affect the whole character, behavior, metabolism, and even the appearance of an animal, just as pregnancy stimulates the enlargement of the mammary glands, just as menstruation may effect psychic changes in the female, so all sex manifestations have their repercussions throughout the whole dog. Knowledge of the structures and purposes of the endocrine glands and their products, the hormones, is of relatively recent date in biology. Even today, such knowledge is far from complete. It seems highly probable that the procreative instinct is brought into play by the hormones of the endocrine glands; and, again through them, the organism is affected by that instinct and by whether or not it is indulged.

Sex and the sexual apparatus cannot be considered as something apart, a mere adjunct to the animal. Sex is a part of the very warp and woof (!) of the dog's being.

We have seen in this chapter how the sperm, bearing the ancestral material from the male dog, is proliferated in the testes, is stored in the epididymis, expelled from there into and through the vas deferens, is bathed and activated by the secretions from the prostate gland, and is ejaculated into the vagina of the bitch. We have seen how, propelled by its lashing tail, it makes the long journey through the uterus into the oviducts to meet and fertilize the ripe ova deposited there from the ovaries. Of the fertilization and the gestation which follows it we shall learn in the ensuing chapter.

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