5. For the most part the girls resemble their mother, and the boys their father; though the contrary is often the case, and the females resemble their father, and the males their mother, and the different parts of the body resemble either parents. Twins have sometimes no resemblance to each other, but they are generally much alike; and one woman cohabited with a man, and conceived seven days after parturition, when she bore a child as like her former as if they had been twins. Some women, as well as other creatures, produce young resembling themselves, others bear those which resemble the male, as the horse called Dicæa in Pharsalia. CHAPTER VII. 1. The seminal fluid in its emission is preceded by wind. The manner of its emission exhibits this; for nothing is expelled to a great distance without pneumatic force. If the seminal fluid is taken up by the uterus and retained there, it becomes inclosed in a membrane. For if it is expelled before it becomes articulated, it appears like an ovum inclosed in a membrane, but without any shell, and the membrane is full of veins. All animals, whether furnished with fins, feet, or wings, whether viviparous or oviparous, are produced in the same manner, except that the umbilicus in viviparous animals is turned towards the uterus, and in others to the ovum; and in some cases both ways, as in a certain kind of fish. Some of them are surrounded by a membrane, others by a chorion. First of all, the fœtus is contained within the last envelope. Then there is another membrane over this, which is in part united to the matrix and is partly separate, and contains water. Between these is a watery or sanguineous fluid, which in women is called prophorus. 2. All animals that have a navel increase by the navel; and in those which have acetabula the navel is united to the acetabulum; and in those which have a smooth uterus the navel is united to the uterus upon a vein. The position of all quadrupeds in the uterus is stretched out; that of fishes is on the side; bipeds, as birds, are folded together. The human fœtus lies folded up with its nose between its knees and its eyes upon them, and its ears turned outwards. All animals are alike in having the head placed upwards at first. As they grow, the head turns round, and the birth of all animals is naturally with the head forwards: for even in those that are folded together the presentation of the feet is unnatural. The embryo of quadrupeds contains excrementitious matter, as soon as it is matured, both fluid and solid. The latter is contained in the extreme parts of the intestine, the former in the bladder.