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.