8. Reproduction by simple division or budding leads to a kind of ‘immortality,’ since each descendant cell is continuous, in a sense, with the original one.
9. This simple division or virgin-birth process may go on to many generations—even to hundreds among the Protozoa.
10. But since at some time or other conjugation is apparently necessary in order to restore vitality, the immortality at this point ceases to be an individual immortality, and becomes rather a joint or racial immortality.
11. The main thing in conjugation would appear to be that the two factors should be complementary to each other, however differentiated, so that in their union the whole race-life should be restored, and the Regeneration therefore be complete.
12. The special sex-differentiation called male and female depends on the separation of the active from the sessile qualities (and other qualities respectively related to each) into two great branches.
13. Since the female takes the sessile part she appears sometimes as the goal and object of conjugation, and the more important factor; but actual observation so far shows each factor, male and female, to be equally important.
14. In the fertilized ovum there are an equal number of chromosomes derived from each parent; and if the female provides the shrine in which the new development takes place, the male (centrosome) appears as the organizing genius of the process.
15. This process, by which a fertilized germ-cell divides and redivides, and so builds up a “body,” is quite similar to that by which a protozoön divides and redivides to form a numerous colony.
16. A ‘body’ indeed is such a colony, coöperatively associated in definite form, of which all the millions of cells are practically continuous with the original fertilized germ, and one with it.
17. Every cell in such a body has apparently the same nuclear elements as the original cell, equally derived from both parents; but is differentiated so far as to be able to fulfil its special part in the body.