THE "sexual season" OF MAMMALS. 25 



Among the deei- in tlie Zoological Gardens their generativ^e 

 activity appears to have been universally stimulated — they will 

 be referred to under the heading of ^' Duration of the Sexual 

 Season in Poly oestrous Mammals/'- — for it would seem that their 

 normal (as I have considered it) monoestrous sexual season is 

 increased by the conditions of captivity until it may become a 

 continuous polyoestrous sexual season. 



The Barbary wild sheep, on the other hand, does not appear 

 to be affected by captivity ; it exhibits a single monoesti-ous 

 sexual season only, each year (Zoo.), and that is probably its 

 condition in the wild state if we may judge from what is known 

 of 0. argali, and 0. burrhel in Tibet (Prejevalsky, 1876). 



It is with some hesitation I have included among monoes- 

 trous mammals deer, sheep, and pigs in the wild state ; their 

 retention in this class is doubtful ; but if these animals were 

 omitted there remains a remarkable series of examples of the 

 variability of the sexual season of monoestrous mammals 

 under various conditions. 



The Duration of the Sexual Season in Polyoestrous 

 Mammals in the Absence of the Male. 



The duration of the sexual season in these animals depends 

 upon two factors, the length of the dioestrous cycle and the 

 number of times it recurs. Both factors may be different in 

 different species of animals, and either may be different in 

 different individuals oF some species, or variable in the same 

 individual at different times. 



Knowledge of polyoestrum in animals in a wild state in 

 this country is limited to certain rodents. The rat (M. 

 decumanus), mouse (M. musculus), and the rabbit in this 

 country are known to experience a recurrence of the dioes- 

 trous cycle. It is probably recurrent also in M. minutus, 

 M. sylvaticus, M. rattus, Arvicola agrestis, A. glare- 

 olus, and Lepus timidus; while possibly Mustela vul- 

 garis and Lepus variabilis, under favourablecircumstances, 

 may also experience a recurrence of the dioestrous cycle, 

 judging from the account given of them by Bell (1874). 



