f two kinds of specialised cells, and these two kinds
are carried about by separate individuals. In some species--fishes,
for example--the two kinds of special cells meet outside the bodies of
the parents. At this humble level the sexes are in many cases very
like one another, and there is, as we should expect, a good deal of
haphazard in the production of offspring. Among fishes, for instance,
the eggs and sperms are liberated into the sea, or the shallow bed of
a river, and, if the sperms (the milt of the males) are placed near to
the spot where the eggs (the spawn) have been laid, fertilisation
occurs, for within a short distance the sperms are attracted--in a way
that is imperfectly understood--to enter the eggs. By this method
there is of necessity great waste in the production of offspring, many
thousands of eggs are never fertilised. The union of the sexual cells
must be something more than haphazard for further development. There
must be some reason inherent in the female or male inducing to the act
of reproduction. In other words, there must be a psychic interest
preceding the sex act. In this way a higher grade is reached when the
presence of one sex attracts the other. Gradually the female and the
male begin to associate in pairs.

We may illustrate this important step in the evolution of love by
reference to the familiar case of the salmon. The male courts the
female and is her attendant during the breeding season, fertilising
the deposited ova in her presence. He guards her from the attention of
all other males, fighting all rivals fiercely, with a special weapon,
developed at this time, in the form of a hooked lower jaw with teeth
often more than half-an-inch long. Darwin records a case, told to him
by a river-keeper, where he found three hundred dead male salmon, all
killed through battle.[44] Thus even among cold-blooded fishes (though
it may appear folly to use the word "love" in this connection) a very
clear likeness with our human sex-passions can be traced.

Sex differences now become more frequent. The males are in some cases
distinguished by bright colours and ornamental appendages. During
their amours and duels certain male fishes flash with beautiful and
glowing colours. Reptiles exhibit the same form of sexual-passion, and
jealous combat of rival males. The rattle of certain snakes is
supposed to act as a love-call. Snakes of different sexes appear to
feel some affection for each other when con