Hermaphroditism must be regarded as a temporary or transitional form.[40] It is found persisting in various degrees in many species—snails, earth-worms, and leeches, for example, can act alternately as what we call male and female. Other animals are hermaphrodite in their young stages, though the sexes are separate in adult life, as, for example, tadpoles, where the bisexuality of youth sometimes linger into adult life. Cases of partial hermaphroditism are very common, while in many species which are normally unisexual, a casual or abnormal hermaphroditism occurs—this may be seen in the common frog, and is frequent among certain fishes, when sometimes the fish is male on one side and female on the other, or male anteriorly and female posteriorly.[41]
There would seem to be a constant tendency to escape from these early and experimental methods of reproduction, and to secure true sexual union, with complete separation of the sexes and differences in the parents. We have noticed the many instances of tiny complemental males, in connection with hermaphrodite forms, which, as Darwin states, must have arisen from the advantage ensuring cross-fertilisation in the females who harbour them. Even among hermaphrodite slugs we find very definite evidence of the advance of love; and in certain species an elaborate process of courtship, taking the form of slow and beautiful movements, precedes the act of reproduction.[42] Some snails, again, are provided with a special organ, a slightly twisted limy dart, which is used to stimulate sexual excitement.[43] What do such marvellous manifestations, low down in the ladder of life, go to prove, if not that there must be the closest identity between the development of life and the evolution of love?
These examples of hermaphrodite love lead us forward to a further step, where no reproduction takes place without the special activity and conjugation of 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 confined together in cages. Romanes relates the interesting fact that when a cobra is killed, its mate is often found on the spot a day or two afterwards. Darwin cites an instance of the pairing in spring of a Chinese species of lizard, where the couples appear to have considerable fondness for one another. If one is captured, the other drops from the tree to the ground and allows itself to be caught, presumably from despair.[45]
A further development is reached by those animals among whom what has well been called "the note of physical fondness" is first sounded. We find the males playing with the female, wooing and caressing her, it may be dancing with her. The love-play is often extraordinary,[46] as, for instance, in the well-known case of the stickleback. Not only does the male woo the female with passionate dances, but by means of its own secretions it builds a nest in the river weeds. The males at this season are transformed, glowing with brilliant colours, and literally putting on a wedding garment of love. The stickleback is passionate, polygamous and very jealous of rivals. His guardianship of the nest and vigilance in protecting the young cannot be observed without admiration.
It is certainly significant to find one of the earliest instances of genuine parental affection exhibited by the male. This reversal of the usual rôle of the sexes is common among fishes, among whom care of offspring is very little developed. In some species the eggs are carried about by the father—the male sea-horse, for instance, has a pouch developed for this purpose; in other cases the male incubates, or cares for the ova. Sometimes, however, it is the female who performs this duty, but the known cases are few.[47] Some exceedingly curious examples of male parental care occur among the amphibians. One of the most interesting is that of the obstetric frog, where the male helps to remove the eggs from the female, then twists them in the coils around its hind legs and buries himself in the water, until the incubation period is over and the tadpoles escape and relieve him of his burden. In other species the croaking sacs of the males, which were previously used for amatory callings, become enlarged to form cradles for the young. There are also instances of the female co-operating with the male in this care of offspring. Thus in the Surinam toad the male spreads the ova on the back of the female, where skin cavities form in which the tadpoles develop. In other cases the eggs are carried in the dorsal pouches of the females. It would almost seem that in this early time Nature was making experiments as to which parent was the better fitted to rear and protect the young!
But let us return to our present examination of animal love-making. In many diverse forms there is a very remarkable courtship of touch, often prolonged and with beautiful refinements, before the climax is reached, when the two bodies unite. Racovitza[48] has beautifully described the courtship of the octopus, which is carried out with considerable delicacy, and not brutally as before had been believed.
"The male gently stretches out his third arm on the right and caresses the female with its extremity, eventually passing it into the chamber formed by the mantle. The female contracts spasmodically, but does not attempt to move. They remain thus about an hour or more, and during this time the male shifts his arm from one viaduct to the other. Finally, he withdraws his arm, caresses her with it for a few moments, and then replaces it with his other arm."
The various phenomena of primitive animal courtship may be illustrated further by the love-parades of butterflies and moths, the love-gambols of certain newts, the amatory serenading of frogs, the fragrant incense of reptiles, the love-lights of glow-worms, the duels of many male beetles and other insects, many of whom have special weapons for fighting with their rivals. Among insects the sexes commonly associate in pairs, and it seems certain there is some psychic attraction added to the primitive tactile courtship. In some cases the association of the sexes is maintained for a lengthened period, with many hints of what must be regarded as love. There are many examples also of parental forethought, amounting sometimes to a sort of divining pre-science, as the habit of certain insects in preparing and leaving a special nourishment, different from their own food, for the sustenance of the future larvæ. We even find instances of co-operation of the sexes in work together, affording a first hint of this linking-force to the development of love in its later and full expression. Such are the activities of the dung-rolling beetle, where the two sexes assist each other in their curious occupation. The male and female of another order of beetle (Lethrus cephalotes) inhabit the same cavity, and the virtuous matron is said greatly to resent the intrusion of another male.[49]