36 THE PHYSIOLOGY OF REPRODUCTION 



Marsupials, is extremely short, the young being transferred at a very 

 early stage of development to the mother's pouch, as in tlie case of 

 Echidna} 



The kangaroos in the Zoological Society's Gardens in London are 

 stated to display sexual excitement in September, and also in April. 

 At such times a slight flow of mucus, which may be tinged with a 

 little blood, has been observed passing from the aperture of the 

 vagina.^ It would appear, therefore, that Tsangaroos may breed twice 

 a year. Unfortunately, there is no positive information available as 

 to whether oestrus recurs during the same sexual season (see below). 



The Marsupial cat (Dasyurus viverrimis) is monoestrous and has 

 one breeding season a year, which begins in May or early June and 

 extends over the winter in Australia, until the first fortnight in 

 August.^ The prooestrum lasts from four to twelve days, and during 

 this time the lips of the cloaca become swollen, and the pouch enlarges 

 slightly and becomes tumid and moist. There are corresponding 

 internal changes (see below, p. 106). (Estrus lasts for one or two days. 

 Pregnancy is stated to last not less than eight and not more than 

 fourteen days. In its absence pseudo-pregnancy occurs, and is 

 accompanied by a series of changes in the reproductive organs and 

 mammary glands essentially similar to those taking place in gestation. 

 The pouch enlarges and the sebaceous, sweat, and mammary glands 

 also hypertrophy as well as the internal organs (see p. 616). At the 

 end of the period the animal has been seen to clean out its pouch for 

 the reception of young, showing that the developmental and cyclical 

 changes of the sexual organs may extend even to the instincts 

 associated with parturition and the nursing of the young, although 

 true pregnancy had not taken place {of. rabbit, p. 576). The anoestrum 

 in Dasyurus lasts more than half the year. 



Hill states that the opossum {Didelphys aurita) has two breeding 

 seasons ; one in June to July, and the other at the end of October. 

 The Virginian opossum, on the other hand, has only one sexual season 

 and one oestrus. Trichosurus vulpecula and Macropus ruficollis 

 breed twice a year, the former in April and September, the latter in 

 August to September and December to February.* 



' In the bandicoot {Perameles) the young are nourished by an allantoic 

 placenta similar to that of the higher Mammals (see p. 419). This is exceptional 

 among Marsupials. 



2 Wiltshire, "The Comparative Physiology of Menstruation," Brit. Med. 

 Jour., 1883. 



3 jjiii and O'Donoghue, "The Keproduetive Cycle in the Marsupial 

 Da^ywras viverrinus" Quar. Jour. Micr. Science, vol. lix., 1913. 



* Hill, " Some Observations on the Early Development of Didelphya Wwrita " 

 (Contributions to the Embryology of the Marsupialia, V.), Quar. Jour. Micr. 

 Science, vol. Ixiii., 1918. See also below, p. 106. 



