2. In some, also, the os uteri is closed, either from the period of birth, or in consequence of disease. Sometimes this is curable, and sometimes not so. It is not, however, difficult to ascertain the state of the case, for it is not possible either to receive or to emit anything in a proper manner. If it appears to have received and rejected the seminal fluid of the male, it is an evidence of the presence of the disease. But those who have no impediment in the way of conception, but are, as it has been said, as they ought to be, unless the man is impotent, or they are not able to have children together, being unable to emit their semen at the same time, and differ very much, such persons will have no children. CHAPTER V. In order to understand of sterility in the male, we must take other symptoms. These will appear very easy, if he copulates with other women, and impregnates them. When the sexes do not appear to concur with each other, although all the before-mentioned circumstances are present, they do not have children together. For it is evident that this is the only reason of sterility: for if the woman contributes to the semen and generation, it is evident that both the sexes should be concurrent: for if the man is quick, and the woman slow, in the emission of the semen (and many women are comparatively slow), this will prevent conception; for which cause they do not produce children by sexual union with each other. They do so, however, when they happen to be concurrent with each other; for if the woman is desirous, and prepared for the intercourse, and is inclined for it, but the man is suffering previous pain, and of a cold disposition, it is then also necessary that they should be concurrent. CHAPTER VI. It is quite plain when animals desire sexual intercourse; for the female pursues the male, as hens pursue the cock and place themselves beneath him, if the male is not desirous. Other animals also do the same. But if all animals appear to have these affections with respect to sexual intercourse, it is plain that the causes must be the same throughout. This bird, however, has not only the desire of receiving, but also of emitting semen. This is a proof of it. If the male is not present, she will emit the semen into herself, and become pregnant, and produce barren eggs, as if she desired both to emit semen, and when she had done so, soon ceased, just as when the male was present. Others also do the same, for a person has attempted to rear some singing locusts, which he had taken in a young state. When grown, they became pregnant spontaneously.