Elephantulus going into anoestrus; menstruation and abortion

Elephantulus myurus jamesoni comes into oestrus at the end of July or beginning of August. For most animals the breeding season ends in January. Some animals may go into anoestrus in December, others only in March. During the breeding season ovulation, fertilization, pregnancy, parturition, post-partum ovulation and fertilization follow each other without interruption or mishap. As at the end of the season also the males go into anoestrus (see a following paper by Miss Z. Stoch, p. 99), a female then often ovulates without being fertilized; the result is a true menstrual cycle. The female may go into anoestrus at any time at the end of the season, independent from the stage in which she happens to be, except that a menstrual cycle, once started, will be completed. Young animals may go into anoestrus directly on reaching sexual maturity; they may menstruate first or become pregnant. Similarly, an old animal may go into anoestrus directly after parturition, but it may also ovulate, menstruate or become pregnant before going into anoestrus. When anoestrus sets in, a pregnancy can be interrupted by abortion at any stage of the development of the embryo. The events observed in E. myurus jamesoni have been compared with similar phenomena in other mammals. Reasons have been given why the phenomena, described in Elephantulus, must be considered to be a real menstrual cycle.