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Dasyurus is monœstrous and has one breeding season a year, which begins at the end of May or early in June and lasts into the first fortnight in August (i.e. it extends over the winter months). The male does not appear to experience a marked rutting season. Copulation is similar to that of Didelphys (Selenka), and the sperms can remain alive in the Fallopian tubes for at least two weeks. Anœtrus.--The anœstral period lasts more than half the year. Pro-œstrus.--Pro-œstrus appears to extend over a varying period of from four to twelve days. During this time, the lips of the cloaca become swollen, the pouch enlarges somewhat and becomes slightly tumid and moist, and the Graafian follicles increase in size and become vesicular. The uterine mucosa increases in thickness and becomes more vascular, its glands lengthen and become convoluted and the uterine epithelium also tends to thicken. Œstrus.--Œstrus lasts usually for one or two days and is the period during which copulation occurs. The changes already initiated during pro-oestrus in the various parts of the reproductive system are continued without interruption. Post-œstrus.--Post-œstrus, which term we employ to designate the period following œstrus and terminated by ovulation, occupies as a rule about five or six days. The tumidity of the cloacal lips disappears, but the changes in the pouch and uterus still continue, not, however, very actively. In the ovary (1) the ova give off the first polar body and the spindle for the second meiotic division is formed. (2) The follicles attain maturity and ultimately rupture, setting free the ova. Ovulation.--Ovulation marks the end of this period and occurs generally about five or six days after cestrus. It is spontaneous and independent of copulation and is remarkable because of the large number of ova liberated. Ovulation is succeeded (a) by pregnancy or (b) by pseudo-pregnancy. Pregnancy.--Fertilisation is effected in the upper part of the Fallopian tube and the second polar body is there given off. As a rule more young are born than can possibly survive owing to the limited accommodation in the pouch. The gestation period is not less than eight and not more than fourteen days, but the interval between copulation and birth is usually considerably longer. Corpora lutea are formed and persist throughout the greater part of the time that the animal is lactating. Nursing Period.--This period may be divided into two phases. (1) Period of Fixation.--A period, lasting for seven or eight weeks, during which the young are firmly attached to the teats. (2) Free Period.--A period of eight or nine weeks when the young are free in the pouch but dependent on the mother for food. After this time the various organs gradually return to a state of rest. Pseudo-pregnancy.--We have applied this term to the period following ovulation iu cases where the ova have failed to develop, because of the occurrence in it of a series of changes in the reproductive organs essentially identical with those met with in pregnant females. Corpora lutea are formed in the ovaries which are identical with those in the pregnant female. The pouch enlarges, and its sweat and sebaceous glands reach a state of hypertrophy and functional activity comparable to that in the pregnant female. The mammary glands also enlarge and reach a state of development equal to that in a female thirty-six hours after parturition. The uteri enlarge and become vascular, often to a marked degree. The uterine mucosa undergoes a series of changes, progressive, regressive and regenerative. Metœstrus.--This is an indefinite period during which the whole of the reproductive organs return to a state of rest.

The Reproductive Cycle in the Marsupial Dasyurus viverrinus