These prolongations meet, and their sides absorb each other at the point of contact; then the protoplasms of the two elements mingle, and at length the two cellules melt into a single reproductive cellule (Spirogyra longata).
Between this marriage of two lower vegetal cellules, which realises to the letter the celebrated biblical words, "they shall be one flesh," or rather one protoplasm, and the fundamental phenomenon of fecundation in the superior animals, including man, there is no essential dissimilarity. The ovule of the female and the spermatozoon of the male become fused in the same manner, with this difference only, that the feminine cellule, the ovule, preserves its individuality and absorbs the masculine cellule, or is impregnated by it.
But, simple as it is, this phenomenon of fecundation is the sole reason of the duration of bi-sexual species. Thanks to it, organic individuals that are all more or less ephemeral,
"Et, quasi cursores, vitaï lampada tradunt."
(Lucretius, ii. 78.)
For many organised beings reproduction seems in reality
the supreme object of existence. Numbers of vegetables
and of animals, even of animals high in the series—as insects—die
as soon as they have accomplished this great duty.
Sometimes the male expires before having detached himself
from the female, and the latter herself survives just long
enough to effect the laying of eggs. Instead of laying eggs,
the female cochineal fills herself with eggs to such a degree
that she dies in consequence, and the tegument of her
body is transformed into a protecting envelope for the
eggs.
At the not very distant time when animism reigned supreme, these facts were attributed to calculations of design. Nature, it was believed, occupied herself chiefly with perpetuating organised species; as for individuals, she disdained the care of them. We now know that Nature, as an anthropomorphic being, does not exist; that the great forces called natural are unconscious; that their blind action results, however, in the world of life, in a choice, a selection,
