GENERATION AND DEVELOPMENT 691 



panionship of the males of her own species. In all animals it is 

 only during the actual period of oestrus or desire that copulation 

 is permitted, and in all polyoestrous domestic animals this period 

 is variable in extent. 



Changes in the Uterus during Sexual Excitement. — During 

 procestrum there is an increase in the uterine stroma, injection 

 of the mucous membrane in consequence of a dilatation of the 

 capillaries, and usually a breaking down of the walls of the latter, 

 leading to extravasation of blood into the stroma, or even into 

 the cavity of the uterus. The glands of the uterus swell and 

 pour out a slight secretion. In some animals, such as the 

 monkey, the epithelial lining of the uterus is destroyed during 

 this period ; but with ungulates desquamation of the uterus is 

 probably very rare, while in carnivores it occurs more or less 

 in every case. The pigmentation found in the mucous mem- 

 brane of the uterus after oestrus is due to the extravasation of 

 blood ; this blood is also the source of the blood-stained dis- 

 charge, and on a more extensive scale is the cause of the menstrual 

 flow in monkeys and women, in both of which there is in addition 

 blood collected in lacunse in the wall of the uterus and destruction 

 of the epithelium. Gradually in all animals the uterus recovers 

 its normal appearance, prooestrum passes away, and is followed 

 by oestrus. Bearing in mind the rapidity with which cestrus 

 may follow prooestrum in such animals as the mare, cow, and 

 sheep, it is evident that the whole of the above process cannot 

 always be fully gone through ; but in the dog, whose cycle is 

 far more regular, the uterus undergoes the changes described. 



By systematically preventing animals from breeding, the 

 sexual season may be interfered with to the extent of complete 

 cessation (Heape). Certainly the mare used late in life for 

 breeding purposes often proves barren. Yet there are mares 

 which, though deprived of the services of the male, never lose 

 their desire, and may for the greater part of their life be a source 

 of danger from sexual excitement. 



Rutting. — When male animals suffer from a periodic sexual 

 excitement, it is known as rutting. This term should be con- 

 fined entirely to a male sexual season, such as is experienced 

 by the camel, stag, elephant, and ostrich. In the rutting stag 

 the neck becomes enormously swollen (Leeney) , the elephant and 

 camel experience a discharge from the temporal gland, and the 

 ostrich becomes red in the legs. All these are at this time 

 dangerous to approach, and frequently violent and aggressive. 



Marshall has shown* that a male generative cycle is present 

 in many animals, though not obvious in those under domestica- 



* 'The Male Generative Cycle,' F. H. A. Marshall, M.-D., Journal of 

 Physiology, vol. xliii., 191 1. 



