28 WAIiTER HEAPE. 



during- September aud October^ accordiug to Cameron (1900) 

 six weeks, wliile in this country September is the sexual 

 mouth for the fallow deer, and July and August the time 

 when the roe deer will receive the male. 



In all these cases there can be little over three weeks 

 during which copulation takes place, and the extremely 

 limited period during which parturition occurs strongly 

 corroborates the view that this is the extent of the usual 

 time during which sexual intercourse is possible. The fact 

 that in captivity three weeks is the usual period which 

 intervenes between two oestri in such animals, and the 

 extreme probability that individual females do not all ex- 

 perience oestrus at exactly the same time (Camerou, 1900), 

 predispose one to believe that they are monoestrous in the 

 wild state ; but, if the limit of time for coition is three weeks, 

 there is still just time for the females to undergo two dioes- 

 trous cycles, and it is this possibility which prevents positive 

 assertion on the matter. 



Among captive animals (Zoo.) not more than two dicestrous 

 cycles have been observed in the gnu during one sexual 

 season. Gazelle dorcas has two or three; the giraffe about 

 three ; while the eland, nylghau, and waterbuck have a 

 series of dioestrous cycles, each lasting three weeks, during 

 May, June, and July each year. 



The gayal and bison, the axis and wapiti deer, on the 

 other hand, experience a continuous series of dioestrous cycles 

 all tiie year round, at intervals of about three weeks. 



The hippopotamus at present in the Gardens is an old 

 animal ; for long she showed no signs of a sexual season, but 

 lately she has done so at irregular intervals; no doubt in her 

 case captivity has checked the generative function, for a 

 former specimen which bore three young while there is said 

 to have exhibited monthly sexual excitement (Wiltshire, 1883). 



Among wild rodents in this country, recurrent dioestrous 

 cycles last about two months, probably, in Lepus variabilis; 

 about three mouths, probably, in Arvicola agrestis; from 

 four to six months, probably, in Mus minutus; about nine 



