Ovaries, Uterus, and Mammary Glands in Rabbit. 435 



Further, it is stated that the degenerative changes in the uterine mucosa of 

 the marsupial instead of preceding ovulation, as they do in the dog, take 

 place after ovulation during a period which, in the non-pregnant animal, is 

 designated the period of pseudo-pregnancy. The differences in the repro- 

 ductive cycles are shown in the following scheme drawn up by Hill and 

 O'Donoghue : — * 



(1) DASYTJRT78. (2) EUTHEEIAN. 



Ancestrus. Ancestrus. 



I ' I 



Pro-cestrus. Pro-oestrus (uterine degeneration). 



I I 

 CEstrus. CEstrus (ovulation). 

 I I 



r 



Post-oestrus (ovulation). Metoestrus. 

 I . 



Pregnancy. Pseudo-pregnancy Pregnancy, 



(uterine degeneration). 



Nursing period. Metoestrus. Nursing period. 



L r J -L r _ 



Ancestrus. Ancestrus 



Hill and O'Donoghue express the opinion that the degenerative changes 

 seen in Dasyurus during the pseudo-pregnant period are equivalent to those 

 which take place in the Eutherian during the pro-oestrum. They suggest 

 that the shortening of the cycle in the Eutherian may have induced an 

 increased growth of the mucosa during the pro-oestrum, and that this in time 

 may have conditioned the earlier recurrence of the degenerative and regenera- 

 tive changes, with the result that these have, been shifted forward so as to 

 occur prior to ovulation instead of after it. On the other hand, Hill and 

 O'Donoghue appear to hold the view, which seems to us scarcely consistent 

 with the suggestion just quoted, that menstruation in man is a degeneration 

 of the uterine mucous membrane, due to its being unable to fulfil its purpose 

 owing to the absence of a fertilised ovum. They state, further, that their 

 observations " afford no support to the view that ' menstruation is identical 

 with heat ' nor for the view that ' menstruation in the Primates is the 

 physiological homologue of the pro-oestrum in the lower Mammalia.' " Thus 

 they appear to regard the condition existing in the Primates as directly 

 comparable to that occurring in Dasyurus, and different from the condition 

 found in the dog. 



Our own observations on the rabbit indicate that the changes in the non- 

 pregnant uterine mucosa which take place concurrently with the development 



* In the scheme drawn up Hill and O'Donoghue "Dicestrus" is unaccountably inserted 

 for the non-pregnant Eutherian between "Pro-cestrus" and "Metoestrus." In the 

 scheme as given above, this is omitted, since the dicestrous period, when it occurs in 

 polycestrous animals, supervenes r metoestruni and not before. 



