es an ovum is about 3000
times as large as spermatozoa.[25] The male cellule, differentiated to
enable it to reach the female, impregnates and becomes fused within
her cellule, which, unlike hers, preserves its individuality and
continues as the main source of life.

It is true that exceptions occur, sex-parasitism appearing in both sex
forms, and in some cases it is the female who degenerates and becomes
wholly passive and dependent, but this is usually under conditions
which afford in themselves an explanation. Thus, in the troublesome
thread-worm (_Heterodera schachtii_), which infests the turnip plant,
the sexes are at first alike, then both become parasitic, but the
adult male recovers himself, is agile and like other thread-worms,
while the female remains a parasitic victim without power of
function--a mere passive, distended bag of eggs. Another extreme but
well-known example is that of the cochineal insect, where the female,
laden with reserve products in the form of the well-known pigment,
spends much of its life like a mere quiescent gall on the cactus
plant; the male, on the other hand, is active, though short-lived.
Among other insects--such, for example, as certain ticks--a very
complete form of female parasitism prevails; and while the male
remains a complex, highly active, winged creature, the female,
fastening itself into the flesh of some living animal and sucking its
blood, has lost wings and all activity and power of locomotion, having
become a mere distended bladder, which, when filled with eggs, bursts
and ends a parasitic existence that has hardly been life.[26] In many
crustaceans, again, the females are parasitic, but this also is
explained by their habit of seeking shelter for egg-laying
purposes.[27]

The whole question of sex-parasitism as it appears in these first
pages of the life-histories of sexes is one of deep suggestion; and
one, moreover, that casts forward sharp side-lights on modern sex
problems. In some early forms, where the conditions of life are
similar for the two sexes, the male and the female are often like one
another. Thus it is very difficult to distinguish a male starfish from
a female starfish, or a male sea-urchin from a female sea-urchin. It
becomes abundantly clear that degeneration in active function, whether
it be that of the male or the female, is the inevitable nemesis of
parasitism. The males and females in the cases we have examined may be
said to be martyrs t