26 WALTt:ii HEAPE. 



In Southern Biivope and Algiers polyoesti-uui is apparently 

 usual amongst rodents (Lataste, 1887). It appears to be 

 ascertained for Sciurus vulgaris living in that part of the 

 world — though the same animal is probably moncestrous in 

 this country — for Eliomys quercinus,, Gerbillus hirtipes, 

 Dipodillus campestris, D. simoni, Meriones shawi, 

 M. longifrons, Mus musculus, M. rattus, M. decu- 

 man us, and to be probably true also for several other species. 



The animals on which these observations were made by 

 Lataste were kept in captivity, but there is good reason 

 to think that the conditions under which they were kept did 

 not interfere with their habits in this respect. 



Among domesticated animals polycestrum occurs in horses, 

 cattle, sheep, and pigs. While for wild animals in captivity 

 it has been observed (Zoo.) in the gayal and bison; in 

 wapiti, axis and red deer ; in the gnu, eland, nilghau, and 

 waterbuck ; in Gazelle dorcas, in giraffes, in elephants, and 

 probably in kangaroos. 



In its most complete form polyoestrum occurs in certain 

 monkeys and in the human female ; probably most monkeys 

 are similarly affected, and possibly also lemurs ; in these 

 animals there is a regularly recurrent series of dioestrous 

 cycles throughout the year. 



The Duration of the Dioestrous Cycle varies from 

 five days (exceptional in rodents, Lataste, 1887) to as much 

 as two months (exceptional in mares, and in various wild 

 animals in captivity from time to time. Zoo.). 



The usual length of the dioestrous cycle for rodents is ten 

 to twenty days, and in other animals in which the phenomena 

 has been observed from three to four weeks. In the rodents 

 observed by Lataste (1887) the dioestrous cycle was usually 

 ten days, and in the rat and mouse in this country the same 

 may be said to be approximately true. In the domestic 

 rabbit, however, I find great variability ; while some indivi- 

 duals exhibit oestrus every three weeks fairly regularly, others 

 do so every ten days ; on the whole I think ten to fifteen days 

 is the usual length of their dioestrous cycle. 



