It is clear that the tendency of this process is to prevent the continued multiplication of one stock or line of descent in a pure state. By conjugation different lines of descent—the progeny of different individuals, often brought together from widely separate localities—are blended and fused. And this is, we are led to conclude, a matter of immense importance. To effect this mixture of separate stocks is, as Darwin has shown, a prime purpose of the habits and structures implanted in the very substance of living things, and developed and accentuated in endless ways and with extraordinary elaboration of mechanisms and procedure during the immense lapse of ages during which life has unfolded and developed on this earth. The fusion of different strains by conjugation gives increased variation in the offspring or new generations: for the two parental strains differ more or less, as all living individuals do, from one another. The result of their fusion is different from either parent. In fact, the process of fusion itself causes a disturbance—a readjustment of the living matter—so that completely new variations result and are selected or rejected in the struggle for existence. Either parental strain was perhaps not so suitable to a newly developed change in the surrounding conditions of life as the new blend may be. Thus a more certain and active production of possibly useful variations is provided for than would be the case were the variations of one self-multiplying stock alone presented for selection.
In the case of simple conjugation the cell individuals which fuse or "mate" with one another, and may be called "maters" or "mating cells," are in all respects similar to one another. But we find among the unicellular plants and animals cases in which one of the mating cells, instead of fusing with another straight away, divides into a number of much smaller cells, which are very active in locomotion and are specially produced in order to mate or fuse with the larger cells. The mating cells are called "gametes," and the large motionless mating cells are called "macro-gametes," or "large maters," whilst the small motile mating cells are called "micro-gametes," or small "maters." The former are of the same nature as egg cells or ovules, the female reproductive particles, whilst the latter, the small "maters," are identical in nature with the sperms or spermatozoa or male reproductive particles of higher organisms. In the case of certain parasitic unicellular animals called coccidia, and also in the parasite which causes malarial fever, quantities of small "mating cells" are produced which fuse with or "fertilize" other much larger mating cells. The small "maters" of coccidia have long vibrating tails and minute oblong bodies, and agree closely in appearance and active locomotion with the spermatozoa of higher animals and plants. The large spherical mating cells might be mistaken for the egg cells of larger animals. In the globe animalcule, Volvox globator, we find a transitional condition leading us to the production of small (male) and large (female) mating cells, like those regularly produced by the massive plants and animals which are built up by hundreds of thousands of "cells" or protoplasmic units conjoined and performing different services for the common life. Volvox is one of those simple aquatic organisms which is not a single cell but a group of many cells (some hundred) hanging together—in this case so as to form a hollow sphere. All the cells of an individual sphere are alike, and have originated by division from one first cell. When the "breeding season" arrives one or two cells of the sphere increase in bulk—they become "large mating cells"—in fact, egg cells. At the same time one or two divide (without separating), so as to form packets of minute oblong cells with vibrating tails. These are "small maters," or "spermatozoa." When ripe they separate and swim away to fertilize—that is to say, to fuse with—the large "mating cells" or egg cells of other Volvox spheres. Such a Volvox sphere as I have described is "bi-sexual": it produces both large and small mating cells, both male and female reproductive cells. But sometimes we find that a number of Volvox spheres produce only large mating cells by the swelling up of one or two of their constituent cells. They are, in fact, female Volvox spheres. And other Volvox spheres produce only packets of small mating cells by the splitting and change of one or two of their constituent cells. They are male Volvox spheres.
When we now look at the higher plants and animals formed of aggregations of innumerable cells (all derived from the division of a first cell—an embryo cell or fertilized egg cell) we find that amongst the mass of variously shaped cells forming the "tissues" of these higher organisms some are set apart even in early growth as "mating cells" (gametes or reproductive cells). Usually they are in two groups—namely, the ovary, which includes the large mating cells or egg cells or ova; and the spermary, which includes the cells which break up into small mating cells or sperms. In many animals both ovary and spermary are present in the same individual, but in most of the larger animals (insects, crustaceans, and vertebrates) either the ovary is suppressed, when the creature is called a male, and produces only small mating cells, or the spermary is suppressed, and the creature is a female, producing only egg cells. In both cases there may be a distinct but minute representative of the suppressed organ present and recognizable by its microscopic structure.
The point in this history, which seems to be important and must not be lost sight of, is that the small mating cell is in all the stages cited actively mobile and swims rapidly through water when its producer is an aquatic animal. The large mating cell is quiescent. It is more or less swollen with granular nutrient particles—often vastly so enlarged. It already is acting the maternal part, preparing nourishment for the growing embryo which will develop from its protoplasm when fused with that of the relatively tiny but active male mating cell. And it is certainly very noteworthy that when these two kinds of mating cells become separated in distinct "carriers" (that is to say, produced one without the other in what are called male and female individuals), the primitive character of the mating cells—whichever of the two kinds they be—impresses itself on the complex elaborate many-celled organism in which they arise. The male is the more active, the more disposed to travel. It is always the male who seeks, courts, woos, and attacks the female, as the small mating cells seek and attack the larger mating cells. The character and conduct of the female animal is largely (not without deviations and additions) based on that of the larger mating cell or macro-gamete; she is the one who waits, is sought, is courted, and wooed. And like the egg cells of which she is the vehicle and envelope, she is specially concerned in the provision of nutriment for the early growth of the young.
Courtship, then, seems to have had its foundations very deeply laid, even in the earliest and simplest forms of life—at the time when the principle of the union of the substance of two strains to produce a new generation was established, and when, further, the active, seeking male cell was differentiated from the immobile nourishing female cell.
Amongst the polyps, sea-anemones, and jelly-fish, though we frequently find that there are distinct males and females, there is no courtship. This is connected with the fact that, like plants, they are (excepting the jelly-fish) fixed and immobile. The male cannot "court" the female, because neither of them can approach the other. I once saw in the aquarium at Naples a sudden and simultaneous discharge of a white cloud, like dust, into the water from half the magnificent sea-anemones fixed and immobile in three large tanks. The cloud consisted of millions of the small "mating cells," and were thrown off by the males. They were carried far and wide by the stream running through the tanks. In the sea such a discharge would be carried along by currents, and might fertilize egg-bearing sea-anemones of the same species growing a mile or two away.
It is when we have to do with actively moving animals that "courtship" comes into existence. It has many features and phases, which comprise simple discovery of the female and presentation of himself by the courting male; attempts to secure the female's attention, and to fascinate and more or less hypnotize her, by display of brilliant colours or unusual and astonishing poses or movements (such as dancing) on the part of the male; efforts of the male to attach the female to himself, and deadly, often fatal, combats with other males, in order to drive them off and secure a recognized and respected solitude for himself and his mate. The courtship of many insects, crustaceans, molluscs, fishes, reptiles, birds, and mammals has been watched and recorded in regard to these details. Naturally enough, it is in the higher forms, the birds and the mammals, that there are the most elaborate and intelligible proceedings in regard to the attraction of the female. But when we compare what birds or, in fact, any animal, does with what man does, we must remember that man has, as compared with them, an immense memory, and has also consciousness. All other animals are to a very large extent mere automata, pleasurably conscious, perhaps (in the higher forms), of the passing moment and of the actions which they are instinctively performing, but without any understanding or thought on the subject. They cannot think because, though some of them are endowed to a limited extent with memory, they have not arrived at the human stage of mental development when consciousness takes account of memory, a memory of enormously increased variety and duration.
Man has more and more, as he has advanced in mental growth, rejected the unreasoning instinctive classes of action, and substituted for them action based on his own experience and conscious memory, action which is the result of education—not the education of the school, but that of life in all its variety. But in many things he is still entirely guided by unreasoning mechanical instinct, and in others he is partly impelled by the old inherited instinct, partly restrained and guided by reason based on experience and memory. This makes the comparison of the courting man with the courting animal doubly interesting. We ought to distinguish what he is doing as a result of ancient inherited mechanism from what he is doing as a result of conscious observation, memory, and reasoning.