The second remarkable point has to do with the onesidedness of sexual conjugation, and the complementary nature of the exchange involved. This is truly noteworthy and interesting. It is evident that if the sperm-cell and germ-cell simply coalesced, containing each the amount of chromatin characteristic of the species—say sixteen chromosomes in the case of the human being—the result would be a cell with double the proper amount, _say thirty-two chromosomes_, i.e. _an amount belonging to another species_. “What happens is that each of the reproductive cells, male and female, prepares itself for conjugation _by getting rid of half its_ chromosomes. Two divisions of the nucleus take place, _not_ as in the ordinary fashion of cell-division, when the chromosomes split longitudinally, but in such a way that, in each division, four of the sixteen chromosomes (making eight in all) are bodily expelled from the nucleus and from the cell, when they either perish, or, in some cases, appear to help in forming an envelope of nutritive matter round the germ-cell. These divisions are called ‘maturation divisions,’ and until they are accomplished fecundation is impossible.”[12] Thus the two nuclei, having each their number of chromosomes reduced to half the normal number (in this case to eight), are now ready to coalesce and so form a new cell with the proper number belonging to the species (_i.e._ sixteen). This cell is the commencement of the new being, and, as already described, it divides and re-divides, and the innumerable cells so formed differentiate themselves into different tissues, until the whole animal is built up. Says Professor E. B. Wilson:—“The one fact of maturation that stands out with perfect clearness and certainty amid all the controversies surrounding it, is a reduction of the _number of chromosomes in the ultimate germ [and sperm] cells_[13] to one half the number characteristic of the somatic cells. It is equally clear that this reduction is a preparation of the germ [and sperm] cells for their subsequent union, and a means by which the number of chromosomes is held constant in the species.”[14]