THE "sexual season" OF MAMMALS. 27 



In the domestic mare and cow three to four weeks, and in 

 the domestic slieep and pig two to four weeks is said 

 (Fleming-, 1878) to be the length of the diosstrous cycle, 

 while another authority (EUenberger, 1892) regards three 

 to four weeks as the usual time for all these animals. 



In wild cattle, deer, and antelopes in captivity (Zoo.) three 

 weeks is the usual time. In monkeys it appears to be about 

 one montli in duration (Heape, 1894, 1897, Keith, 1899). In 

 the human female, while twenty-eight days is the normal 

 length of time occupied by the dioestrous cycle, it is fre- 

 quently experienced every three weeks or every live weeks, 

 while occasionally even shorter or longer periods are known. 

 Aristotle is represented to have made the extraordinary state- 

 ment that few women menstruate every mouth, while most 

 menstruate every three months. It would seem possible that 

 the opposite is what he meant; at the same tiuie it should be 

 remarked that various observers (Wiltshire, 1883) have re- 

 corded their opinion that the women of certain tribes in 

 different parts of the world menstruate only at long intervals 

 (see also Ellis). 



The recurrence of the DicBstrous Cycle is also very 

 variable; exact knowledge on this point is not possible for 

 wild animals; only those under observation, captive or 

 domestic, can supply the requisite information. 



The known limitations of the sexual season among certain 

 wild animals, however, admit of a fairly accurate idea being 

 gained of the recurrence of their dioestrous cycles, although 

 not accurately enough to enable one to determine with cer- 

 tainty whether an animal is monoestrous or polycBstrous. 

 For instance, the American bison (Allen, 1876) experiences 

 a sexual season from some time in July until some time in 

 August. In the Cashmir ibex it persists duriug parts of 

 November and December. In the Mark h or and He mi tra- 

 gus jemlaicus in Cashmir it occurs in December, while in 

 the " Barasingh " in that country from September 20th to 

 November 20th it has been observed (Laurence, 1895). 



In Scotland the red deer's sexual season lasts three weeks, 



