It is therefore evident that in order to understand propagation and just what is implied in the act we must make a closer analysis of cell-division, which will be attempted in the next chapters in this book.

Aside from the complex secondary aid which sex has given to the process of propagation among the higher forms of life, the most important fact which has always led to the conclusion that the two must have an elementary relation is the fact of fertilization.

We might easily understand ho...