Professor Rumley Dawson holds to the opinion that the male-determining and female-determining ova are discharged alternately from the ovaries. In woman one ovum is usually discharged each month, and it is maintained that on one month the ovum is male-determining, and in the next, female-determining. It is obvious that exceptions must occur, for boy and girl twins are quite common, but if the cases which support the hypothesis are taken by themselves, and the exceptions explained away, it is possible to make out a strong case in favor of this theory. Some authorities hold that the right ovary produces male-determining ova, and the left ovary female-determining, and that the two ovaries discharge an ovum alternately, but an impartial examination of the evidence for this belief shows that it rests on very slender foundations. Experiments on the lower animals have shown that after the complete removal of one ovary the female may produce young of both sexes. Women, also, have produced children of a particular sex after the corresponding ovary has been removed, and it is hardly possible to believe that the removal in all these cases was incomplete. On the whole it must be concluded that the theory is insufficiently supported by the evidence. Another widely promulgated and vigorously supported theory is that which holds that the sex of the future child may be determined by specific nutrition of the mother before conception, and in some cases after conception. Schenk's theory, advanced about 1900, attracted much attention at the time. He based his method on the observation that a number of women whose children were all girls all excreted sugar in their urine, such as happens in the case of persons affected with diabetes. From this he suspected that the physiological condition which leads to the excretion of sugar was inimical to the development of male-determining ova, and that males could be produced by its prevention. He therefore recommended that those who desire a male child should undergo treatment similar to that prescribed for diabetes for two or three months before conception, and held that a boy would be produced by these methods. Although this method has had considerable vogue, it cannot be held to have been established on a scientific basis.