This psychological thesis has been maintained, in all its rigour, by Delbœuf: “That girl and that young man, in being attracted to one another, obey the will, unknown to both, of a spermatozoid, an ovule. But it may be taken as certain that this will is not unknown either to the spermatozoid or the ovule; both know what they want, and seek it. To this end they give their orders to their respective brains through the medium of the heart, and the brain obeys without knowing why. Sometimes it imagines that it has been convinced by reason and explains its own choice to itself. At bottom it has been but an _unconscious_ instrument in the hand of an imperceptible workman who knew both what he wanted and what he was doing.” (_Revue philosophique_, March 1891, p. 257.) ----- If we confine ourselves to the micro-organisms, these facts of sexual attraction have been interpreted in two ways, as we have already seen—one psychological, the other chemical. Some, as we have just heard, admit a desire, an elective action, a choice, quoting in support of this not only the phenomena of generation, but several others: as the habitat, the use of a certain substance in the formation of the carapace, the movements of certain micro-organisms in seeking and seizing a determined prey. Others reject this psychology, which they call anthropomorphism, and maintain that chemical action is sufficient to explain the whole. Pfeffer had already shown, as far as generation is concerned, that the spermatozoids of the cryptogamia are attracted by certain chemical substances varying according to the vegetable species. More recently, Maupas and Verworn, who have successively studied the alleged cases of choice, eliminate all psychical elements and reduce the whole to a purely mechanical process. I am inclined to adopt the second opinion, while recognising that, as far as problems of origin are concerned, we decide by probabilities rather than proofs. Above this chemical or organic attraction we find the sex-instinct properly so called, which, with its numberless adaptations, embraces the whole animal world. It is useless to prove that this instinct is fatal, blind, not acquired, anterior to all experience; but, as by its nature it consists essentially of motor manifestations, its psychology is scanty enough. Some remarks on this point may not be without advantage. In fact, as regards the problem of instinct, an entirely new position has been taken up.