THE "sexual season OF MAMMALS. 53 



Stage IV for ruminants, horse and pig, and where external 

 bleeding is seen in these animals the occurrence of the 

 equivalent of Stages V and VI is essential. 



Kazzander (1890) notes the existence of extravasated 

 blood (Stage IV) in the sheep^s uterus during pro-oestrum, at 

 a period before external bleeding is noted ; so that when the 

 latter occurs, a condition equivalent to Stage VI is passed 

 through by this animal. Both this author and Bonnet (1880, 

 1882), whom he quotes, describe pigmentation in the uterine 

 mucosa of the sheep, and consider it is due to the extrava- 

 sated blood which is not discharged during the pro-oestrum. 



Lataste (1887) describes desquamation of uterine epithelium 

 in several Muridee, and states that it takes place independently 

 of pro-oestrum, (or, as he calls it, " rut "), during which Stages 

 II and III ai-e noted, and at the close of which a bloody dis- 

 charge (which he calls " menstruation ") is evident. Stages 

 IV, V, and VI are therefore probably also passed through 

 in the case of these animals. 



I find it difficult to detei'mine exactly what this author 

 means, but I gather it is his opinion that in these animals 

 there is a periodic shedding of uterine and superficial vaginal 

 epithelium, and that this precedes and is independent of the 

 pro-oestrous discharge (p. 163) ; if this be so it is quite dif- 

 ferent from anything which has been already described for 

 any other of the lower mammalia, and is comparable only to 

 that somewliat rare phenomenon, exfoliation of the vagina, in 

 the human female. The same author declares (1893) there is 

 a rhythmical transformation of the epithelium of the vagina in 

 certain of the lower mammalia, which is in connection with 

 rhythmical generative changes ; he describes the denudation 

 of this epithelium, and its recuperation from the lower layers. 

 The subject has been very rarely investigated in the lower 

 mammals, and still more rarely has it been attacked from a 

 histological point of view; isolated specimens have been 

 described with more or less detail, but no attempt has been 

 made to work out the history of the process by any one, so 

 far as I know, but Eetterer. 



