THE " SEXUAL SEASON " OF MAMMALS. 21 



from a cow "in season" (i. e. during- oestrus), but whicli has 

 not had the bull, will, if drunk by another cow, bring on the 

 sexual season of the latter (Youatt, 1834). 



That it is associated with a stimulus which is manifested 

 by exceptional vigour and exceptional bodily "condition" 

 is demonstrated by the pugnacity of the males at such times, 

 by the restless activity of the females, by the brilliant 

 colouring of such widely divergent animals as, for instance, 

 annelids, amphibia, birds, and mammals, by the condition of 

 the plumage of birds, and of the pelage or skin of mammals. 



That it is associated with nutrition, and that it is a stimulus 

 which is gradually collected, is indicated by the increased 

 frequency of the sexual season among domesticated mammals 

 as compared with nearly allied species in the wild state. 



That it is manifested by hypertrophy and by congestion 

 of the mucous tissue of the generative organs, and of various 

 other organs, such as the wattles and combs of birds, the 

 crest of the newt; and by the activity of special glands, the 

 affection of all of which may be exceedingly severe, is true. 



These, and many other similar facts, are well known, but they 

 do not assist in the elucidation of the origin of the function. 



The most that they do is to show tli;itthe sexual instinct is 

 seasonal, and that nutrition, whether affected by external or 

 internal factors, plays an important part in its manifestation. 



The Periodicity of the Sexual Season in 

 Moncjestrous Mammals in the Absence of the Male. 



In the absence of gestation most mammals woidd appear to 

 experience at least one sexual season per annum, under natural 

 conditions, but there is great variation in the periodicity of 

 the sexual season in captive and domesticated mammals, the 

 variation being extended not only to varieties of a species, 

 but also to individuals of that species under domestication. 



Among certain wild animals which are known to undergo 

 parturition only during a very circumscribed time, the 

 monoestrous condition may be assumed as probable, and the 

 periodicity of the sexual season calculated; but it must be 



