CHAPTER IV 



TYPES OF (ESTROUS CYCLE 



{a) MARSUPIALS 



Dasyurus. In Dasyurus vivierriniis, studied by Hill and 

 O'Donoghue (300), O'Donoghue (476), and Sandes (544), the 

 anoestrous period lasts more than half the year. This is termi- 

 nated by the onset of the active phase of the reproductive cycle, 

 which is divided by Hill and O'Donoghue into four stages — pro- 

 oestrus, oestrus, postoestrus, and pregnancy or pseudo-pregnancy. 

 During prooestrus, which lasts from four to twelve days, char- 

 acteristic changes occur both in the uterus and in the external 

 genitalia. The marsupial pouch, for instance, enlarges, but 

 according to O'Donoghue no mammary changes occur during 

 oestrus. The uterine mucosa increases in thickness and becomes 

 very vascular, the glands lengthen and become convoluted, 

 while the epithelium tends to thicken. These processes are 

 continued during oestrus, which lasts only for one or two days, 

 and at which time copulation takes place. Ovulation is delayed 

 until the next stage, to which Hill and O'Donoghue gave the 

 name of 'postoestrus'. The length of this phase appears to be very 

 variable, but the authors state that ovulation does not occur 

 until five or six days after the end of oestrus. Ovulation is 

 spontaneous and is remarkable because of the large number of 

 ova liberated. Pregnancy lasts not less than eight and not more 

 than fourteen days. In the absence of conception, changes occur 

 which are essentially the same, and of the same duration, as 

 those during pregnancy. Corpora lutea, indistinguishable from 

 those of pregnancy, are formed in the ovary (544). Typical 

 changes in the mammary glands, the uterus, and the marsupial 

 pouch also occur. As a result of a detailed study of the 

 growth changes in the mammary apparatus, O'Donoghue 

 came to the conclusion that no difference is observable 



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