tions which constitute the indirect effects or derivatives
of the sexual appetite. The most evident of these is _jealousy_, or
the feeling of grief and anger produced in an individual when the
object of his sexual appetite is disputed by another individual of the
same sex. Jealousy may also arise from other instincts, such as those
of nutrition, ambition, etc.; but it forms one of the most typical
complements of the sexual appetite, and leads, as we know, to furious
combats, especially between males, sometimes also between females.

Owing to its profoundly hereditary origin, this passion has a very
instinctive character, and might quite as well have been mentioned in
the preceding chapter. I deal with it here because it is naturally
associated with other irradiations of the sexual appetite, and because
it has a peculiarly mental character.

=Relation Between Love and Sexual Appetite. Sympathy.=--Having entered
the higher brain, or organ of mind, and become modified, complicated,
and combined with the different branches of psychic activity, the
sexual appetite takes the name of _love_, properly so-called. In order
to better understand the relations of love to the sexual appetite we
must refer to Chapter II. Let us begin with a short exposition of the
phylogeny of the sentiments of sympathy, or the altruistic and social
sentiments.

In the lower animals with no separate sexes egoism reigns absolutely.
Each individual eats as much as it wants, then divides, buds or
conjugates, thus fulfilling the sole object of its existence. The same
principle holds in the lower stages of reproduction by separate sexes.
Spiders give us a good example. In these, copulation is a dangerous
act for the male, for if he is not extremely careful he is devoured by
the female, sometimes even before having attained his object, often
soon afterward, in order that nothing may be lost. However, the female
shows a certain consideration for her eggs, and sometimes even for the
young after they are hatched.

In higher stages of the animal kingdom sentiments of sympathy may be
observed, derived from the sexual union of individuals. These are
sentiments of attachment of the male for the female, and especially of
the female (sometimes the male also) for their progeny.

Such sentiments become developed and may be transformed into intense
love between the sexes, of long duration. Birds, for instance, often
remain faithful for many years, and even for lif