_Eichstadt_ also attributes to the uterus an aspiratory force, dependent upon coitus, and competent to force into the interior of the uterus the semen ejaculated into the os uteri. The changes in the uterus which are the necessary antecedents of this aspiration, namely, an engorgement with blood whereby the flattened form of the uterus gives place to a more rounded form, and the cavity of the organ is increased in capacity, take place, in the opinion of this author, only when during intercourse the woman has attained the acme of sexual gratification, by which alone can the aforesaid change in the uterus be brought about. _E. Martin_ and _Chrobak_ have also directed attention to the fact, that some importance in this connexion must be attached to the facultative enlargement in the size of the os uteri externum. _Lott_, by his researches into the behaviour of the cervix uteri in relation to the act of conception, is led to the conclusion that the locomotive capacity of the spermatozoa forms the principal factor in effecting a fertilizing contact between the spermatozoa and the ovum. This locomotive capacity may be increased or diminished by a number of conditions, among which the principal are: the activity of the cervix uteri (the ciliated epithelium); the character of the secretions; and the position, shape, and size of the cervix. Thus, this author concludes, the part played in conception by the normal cervical canal is a purely passive one, with the sole exception of the activity of the ciliated epithelium—and the influence of this factor must be regarded as extremely doubtful. That during ejaculation the external orifice of the male urethra and the os uteri externum are in close apposition, is denied by _Lott_, who adduces in support of his views data derived from comparative investigations on various animals. In the dog, the configuration of the genital organs is such that it is impossible to suppose that any apposition can occur; the same is the case with the sheep; and still more so with the rabbit, who possesses two quite distinct portions vaginales, projecting freely into the vagina. In the human species also, the character of the walls of the cervical canal, where in the normal state the plicae palmatae may almost be said to interlock, separated only by a thin stratum of mucus, offers a hindrance to the entrance of the ejaculated semen by the direct force of ejaculation itself. As regards the independent motile powers of the spermatozoa, the researches of _Lott_ showed that not only can they overcome strong capillary currents, and can traverse the width of a coverglass (18mm.—about ¾ in.) in about five minutes; but further that they are capable of migration through the finest interstices (those of an animal membrane) provided that the fluid with which the membrane is moistened is one favourable to their vital activity.