THE MYSTERY OF SEX/PART 5

 

CHAPTER V

SEX IN ANIMAL LIFE

In animal-life, as in plant-life, we find the male and female elements of reproduction. In animals, the male element of reproduction is called the Spermatozoon; and the female element of reproduction is called the Ovum.

The Spermatozoa (plural of spermatozoon) are the active, moving constituents of the male element of reproduction, and consist of a head, a rod-shaped middle piece, and a long hair-like tail, by the vibratile motion of which they move in a spiral manner. They were formerly regarded as parasites inhabiting the seminal fluid, but were finally discovered to be the fecundating cell or male element of reproduction. They are found in all animals, including man. The size of the spermatozoa varies in different animals. In man they are about one six-hundredth of an inch in length. Their peculiar movements resemble those of the tadpole, the hair-like tail manifesting constant motion from side to side, propelling the spermatozoon from one point to another. It is composed of protoplasm, the substance which is the base of all physical life. The Spermatozoa develop from a mother-sperm-cell, by the progress of segmentation or subdivision, in a manner analagous to that of the lowly forms of animal life. They dwell in a gelatinous fluid, which mingles with other fluids secreted by the glands, and which thus constitute the male seminal fluid.

Geddes gives the following information regarding the physiology of the Spermatozoa. He says:

"A few facts in regard to the physiology of the sperm demand notice, (a) It is specialized as a highly active cell; its minimal size, the usual absence of any encumbering nutritive material, the contractility of the tail, and the general shape, all fit it for characteristic mobility. More than one histologist has likened it to a free muscle-cell, or to a flagellate monad. (b) Furthermore, the sperm has very considerable power of persistent vitality. Not only does it often remain long unexpelled in the male animal, without losing its functions, but it may retain its fertilizing power after remaining for weeks, or even months, in the female organism.

In the earthworm, the spermatozoa pass from one worm to another, not directly to the ova nor to female ducts, but to be stored up in special reservoirs or spermathecae. So it is with many animals. The spermatozoa received by the queen bee during her single impregnation, are for a considerable period -even for three years- used in fertilizing successive sets of worker and queen ova. Quite unique, however, is the case of one of Sir John Lubbock's queen ants, which laid fertile eggs thirteen years after the last sexual union with a male. The spermatozoa had apparently persisted all that time. Hensen cites the facts that a hen will lay fertilized eggs eighteen days after the removal of the cock, and that in bats, spermatozoa may remain alive a whole winter in the uterus of the female. In most European bats, indeed, sexual union occurs in autumn, but the sperms are simply stored in the uterus for ovulation, and fertilization do not take place till spring. In exceptional cases, especially in young forms which were not mature in autumn, pairing occurs in spring. An exactly parallel condition is known in some snakes. Thus Rollinat notes in regard to Tropidonotus viperinus that mature females are inseminated in the autumn previous to the egg-laying (in June or July), but in females laying for the first time, copulation probably occurs in early spring. (c) Remarkable too, and again suggestive of monads, is the power the sperms have of resisting great deviations from the normal temperature. The presence of acids has usually a paralyzing influence, but alkaline solutions have, on the whole, the opposite result."

The Ovum, or female element of reproduction, is a small egg-Iike cell, very small, which is formed in the ovaries of the female, and is afterward passed downward through a duct. Ova are developed from time to time, and pass downward through the duct that they may be fertilized by a spermatozoon or male element.

Geddes gives the following information regarding the physiology of the Ovum. He says:

"The ovum presents all the essential features of any other animal cell. There is the cell-substance, consisting in part of genuine living matter or protoplasm; and there is the nucleus, or 'germinal vesicle,' which plays such an important part in the ripening, fertilizing, and subsequent division of the cell. Besides the living matter, there are simpler substances, especially in many cases a reserve capital of yolk nutriment for the future embryo. The modern masters of microscopic technique have detected many marvels in the egg-cell, into which we cannot at present enter, but it is important to recognize clearly that although the ovum is in a sense simple, being a single cell, it is not structureless like the white of egg. About details there is great diversity of opinion, but all are agreed that the ovum has 'organization.' In many instances, e. g., in the minute ovary of hydra, in the ovary of Tubularia, or in the ovarian tubes of insects, the ovum is but the surviving competitor among a crowd of surrounding cells, which to start with were all potential ova. This is an often forgotten chapter in the struggle for existence, -the struggle between germ-cells. There is a struggle between potential ova; there is also enormous elimination among the spermatozoa, even after they come, to close quarters with the ovum. Many are almost successful, but in most cases only one fertilizes, e. g., survives. And even after the eggs begin to develop there is often elimination apart from enemies, thus it is stated that only about a third of the eggs of the New Zealand 'lizard' (Sphenodon or Hatleria) ever hatch, (c) In the third place, and this is the rarest form, the egg-cell acquires a store of food-material from a special yolk gland, as in many of the lower worms.' "

Fecundation, or reproduction, is caused by the union of the male and female elements -the Spermatozoon and the Ovum. The former enters into and is enclosed by the latter, and the process of the formation, development and evolution of the young life is begun. The union of the two creative cells -the male and the female elements- forms a new and more complex cell, which then develops and evolves into the perfect young of the species to which the parents belong.

In various ways, and by means of various methods and processes, the spermatozoon is brought in contact with the ovum. The act of physical union between the male and female of the higher form of animal life is called coition or copulation -and its sole purpose is that of fecundation and the reproduction of life. It is usually accompanied by a peculiar nervous, spasmodic disturbance, which exhausts the participants to a greater or lesser extent. The spermatozoon comes in contact with the ovum and penetrates the outer covering of the latter, the entrance of other spermatozoa being then prevented by the immediate formation of a thick membrane through which they cannot penetrate.

Geddes gives the following information regarding the physiology of fecundation or fertilization. He says :

"There are various steps in the process which is often summed up in the one word -fertilization. ( I) There is the process by which the spermatozoa are brought into general proximity to the ova. In higher animals this is best termed insemination, and is accomplished by copulation. (2) There is the approach of the spermatozoon to the ovum, but of this little is known. (3) There is fertilization in the strict sense -the intimate and orderly union of the two sex-nuclei.

"The adaptations which secure that the sperms shall reach the ova are very varied. Sometimes it seems almost a matter of chance, for the sperms from adjacent males may simply be washed into the female, as in sponges and bivalves, with the nutritive water-currents. In other cases, especially well seen in most fishes, the female deposits her unfertilized ova in the water; the male follows and covers them with spermatozoa. Many may have watched from a bridge the female salmon ploughing along the gravelly river bed depositing her ova careful to secure a suitable ground, yet not disturbing the already laid eggs of her neighbors. Meanwhile she is attended by her (frequently much smaller) mate, who deposits milt upon the ova. In the frog, again, the eggs are fertilized externally by the male just as they leave the body of his embraced mate. Or it may be that the sperms are lodged in special packets, which are taken up by the female in most of the newts, surrounded with one of the male arms in many cuttle-fishes, or passed from one of the spider's palps to the female aperture. In the majority of animals, e. g., insects and higher vertebrates, copulation occurs, and the sperms pass from the male directly to the female. Even then the history is very varied. They may pass into special receptacles, as in insects, to be used as occasion demands; or, in higher animals, they may with persistent locomotor energy work their way up the female ducts. There they may soon meet and fertilize ova which have been liberated from the ovary; or may persist, as we noticed, for a prolonged period; or may eventually perish. When the sperms have come, in any of these varied ways, in close proximity to the ovum, there is every reason to believe that a strong osmotic attraction is set up between the two kinds of elements. . . . The spermatozoa, which seem so well to deserve Rolph's epithet of 'starved,' appear to be powerfully drawn to the well-nourished ovum, and the latter frequently rises to meet the sperm in a small 'attractive cone.' Often, however, there is an obstacle in the way of entrance in the form of the egg-shell, which may be penetrable only at one spot, well called the micropyle. Dewitz has made the interesting observation that round the egg-shells of the cockroach ova, the sperms move in regular circles of ever-varying orbit; and points out that thus, sooner or later, a sperm must hit upon the entrance. He showed that this was a characteristic motion of these elements on smooth spheres, for round empty egg-shells or on similar vesicles they moved in an equally orderly and systematic fashion. The persistence with which the spermatozoa often force their way to the ova makes it impossible to doubt the reality of a strong chemotactic attraction. One illustration may suffice. Ac- cording to Dr. Sadone's account of the impregnation in the rotifer Hydatina senta the spermatozoa of the male, which are injected into the body-cavity of the female, reach the totally enclosed eggs by boring through the thin membrane at a point where the mature ova are situated -a process not known in any other animals. The oval head of a spermatozoon was seen to attach itself to the membrane of the ovary, the tail continued to make lashing movements, the head was gradually forced through the membrane, and the tail followed, the whole process taking about ten minutes."

In addition to the numerous examples of the various methods and processes of fertilization mentioned by Geddes, as above quoted, we may mention a few unusual examples. Among the most curious is the process of Parthogenesis. In this mess, which is the common method among certain of the plant-lice, the male and female copulate in the usual manner, and the female lays eggs, which in time are hatched. But the young so hatched from the eggs are not normal insects -they are neither male nor female, but are peculiar sexual creatures which may be called "imperfect females." These imperfect females, instead of seeking fertilization from the male, and then laying eggs as did their mother, produce young resembling themselves, by a process of "budding." These "budded" young, then "bud" forth a new generation, and so on until nine generations are born, when a few perfect males and females are produced, and the process begins anew in the normal fashion. Some of the polyps, a low animal form resembling a plant, 'bud" forth young, which then separate and swim about as independent organisms. Instead of developing until they resemble the parent polyp, however, these young, upon reaching maturity, are fertilized and lay eggs, which when hatched produce the original form of polyp, resembling the grandparent. And so on, the generations alternating.

A curious state of affairs is noted in the case of the Bilharzia, a parasitic trematode, the male of which carries the female about with him in a "gynaecophoric canal" composed of folds of skin. Similar to this peculiar case, is that of certain barnacles in which the female carries around with her male mate, secreted in a little pocket-like contrivance. This mate is much smaller than the female, and is very different from the latter in appearance, so much so in fact that it took Science a long time to determine that it was not a parasite. In some cases, the female has been found to carry several of these tiny male mates around with her.

Geddes gives the following additional information on this subject. He says :

"A not unfrequent mode of fecundation is by means of spermatophores, or packets of spermatozoa. These may be seen at times attached to the earthworm, or found within the leech and snail. Even in newts spermatophores may be formed, and taken up as such by the females. In the spider the spermatozoa are stored in a special receptacle on the palp, and hence hastily transferred to the fierce female. In cuttlefishes this mode of impregnation is yet more marked. One of the arms of the male, much modified and laden with spermatophores, is thrust, or in many cases bodily discharged into the branchial cavity of the female, where it bursts. Such a discharged arm was, on first discovery, regarded as a parasite, and hence received the name of Hectocotylus. A curious aberration from the ordinary relations is where two distinct individuals of a species of fluke (Diplozoon) physically combine in almost life-long union. In many cases again, especially in bony fishes, there is a sexual attraction between male and female, but without any copulation. The female, accompanied by her mate, deposits ova, which he thereupon fertilizes with spermatozoa. A slightly more advanced stage is seen in the frog. Fertilization is still outside the body of the mother, but the male, embracing the female, liberates spermatozoa upon the eggs, just as these are laid. In the majority of cases, however, special organs for emitting and for receiving spermatozoa are developed, and copulation occurs. The male organ is often an adaptation of some structure already existing, as in many crustaceans, where modified appendages form external canals for the seminal fluid. In skates and other gristly fishes, the remarkably complex copulatory organs, the so-called 'claspers,' are in close connection with the hind limb. The copulation may be quite external, as in crayfishes, etc., where the male, seizing the female, deposits spermatozoa upon the already laid eggs. Oftener, however, it is internal, and the intromittent organ is inserted into the genital aperture of the female. True copulation may occur without the presence of special organs, -notably in the case of many birds, where the cloaca of the male is opposed to that of the female. The spermatozoa, forcibly expelled by the excited male organs, pass up the female ducts, probably, in part, as the result of peristalsis, but chiefly at least by their own locomotor energy, and one of them may eventually fertilize an ovum. In addition to the intromittent organ, and the lower portion of the female duct which receives it during copulation, there may be auxiliary structures. such as true claspers for retaining hold of the females. The limy 'cupid's dart' or 'spiculum amoris' of the snail, is usually interpreted as a preliminary excitant."