The loves of fish (and also of echinoderms, star-fish, sea-anemones, etc.) thus reduce themselves, in the main, to those of ovule and spermatozoide. The essential. But such simplification is rather shocking to the sensibility of a superior vertebrate, or to an insect accustomed to the amorous parade, to multiple and prolonged contacts, to the presence and complexity of the opposite sex. This fashion of love is, admittedly, not unknown to men, but they seem to be led to it rather by necessity than by taste, by morals rather than by the search for the maximum pleasure. Genital satisfactions obtained apart from contact, apart from being necessarily infecund, save in scabrous scientific experiments, often cause a nervous and muscular depression greater even than excess committed in common. But this result is not so evident that one can convert it into a moral principle, and the fact remains that onanism, carefully considered, is one among nature's gestures. A different conclusion would be more agreeable; but millions of creatures would protest, from all the oceans, and from beneath the reeds of all rivers. One might go further, and insinuate that this method which appears to us monstrous, or, since it is a matter of fish, singular, is perhaps superior to the laborious method of cavalage, so ugly, in general, and so inconvenient. But there is not in terrestrial nature, any more than in conceivable nature a high and low, a wrong side and a right side; there is neither a good nor evil manner, a right nor a wrong, but there are states of life which fulfill their purpose, since they exist and since existence is their aim. Doubtless the discord between the will and the organs is constant in all stages of life, and much accentuated in man where the wishes are multiplex, but where the nervous system remains, in short, the master, and governs even to the danger of its life. It is not the chance of circumstances and of milieu that has swelled the spermoduct of certain fish into papilla, and then into penis, or formed a sheath for this penis at the expense of the caudal fin; it is the will force of cerebral ganglia. The evolution of the nervous system is always in advance of that of the organs, this is a cause of incoherence, and at the same time, of progress and change. The day when the brain has no more orders to give, or when the organs have exhausted their faculties of obedience, the specie is fixed; if fixed in a state of incoherence it moves toward certain extinction, as the monotremes. Many species seem to have been destroyed in full evolution by the contradictory exigencies of a tyrannous and capricious nervous system.