As the progressive evolution of the multicellular organism continued, and there occurred an increasing differentiation of the individual portions of the body, it became necessary that the very simple process of reproduction of the unicellular organism (by simple cell-division or by conjugation) should, in the multicellular organisms of the metazoa, be ensured and facilitated by the development of new apparatus. This was all the more necessary because, owing to the differentiation of the other organs, the originally independent reproductive elements became more and more dependent upon the parent organism, and lost their former capacity for obtaining nourishment by means of their own activity. Hence it became necessary that the period of time elapsing between the moment when the reproductive cells were freed from the parent organism and the moment in which they coalesced to form a new individual should be shortened to a minimum. This purpose is subserved by apparatus which renders possible the =secure= and =rapid= coalescence of the two reproductive elements, having the form of special =excretory canals= with contractile walls, through which the two sexual elements pass. These are the “=copulatory organs=,” by means of which the distance between the two loving individuals is abridged. According to the exhaustive investigations of Ferdinand Simon, the perfection and differentiation of these conducting canals proceeds _pari passu_ with the higher development of the organism. Simultaneously therewith proceeds the differentiation of the proper internal reproductive organs, the rudiments of which are =identical= in the two sexes. A portion of these primitively identical structures undergoes further development in the male, another portion undergoes further development in the female, whilst in both sexes rudiments of the earlier condition are retained, and these bear witness to the primitive state in which =both= reproductive glands were present in a single individual (hermaphroditism). In this sense Weininger’s theory applies--viz., that there is no absolutely male and no absolutely female individual, that in every man there is something of woman, and in every woman something of man, and that between the two various transitional forms, sexual “intermediate stages,” exist. Therefore, according to this view, every individual has in his composition so many fractions “man” and so many fractions “woman,” and according to the preponderance of one set of elements or the other, he must be assigned to one or the other sex. This theory, which Weininger regards as his own discovery, =is by no means new=, and already finds a place in Heinse’s “Ardinghello,” where we read: