THE " SEXLTAL SEASON " OF MAMMALS. 31 



Wild cattle iu captivity (Zoo.) are also capable of repro- 

 duction at any time of tlie year, and they also experience a 

 remarkable increase in the recurrence of their dioestrous 

 cycles, from what we are led to infer, by the limited 

 calving season, is the case among similar animals in the 

 wild state. 



Among domesticated mammals similar modifications are 

 evident, not only in animals of different species, but in indi- 

 viduals of the same species, as, for instance, in cattle and 

 horses. 



Mares may have only one period of oestrus in the year, in 

 which case they are purely monoestrous animals, but this is a 

 rare condition; rarely, also, they may have two dioestrous 

 cycles, but usually they have many. In the latter case oestrus 

 may recur every three weeks, or the interval may be longer. 

 As a rule among thoroughbred mares the history of the 

 sexual season shows a series of dioestrous cycles, each occupy- 

 ing about three weeks and recurring throughout the spring 

 and often until the early autumu, as many as seven or eight 

 months being in some cases thus occupied. 



Although these animals — horses, cattle, and deer — either 

 in captivity or under domestication, experience such an ex- 

 tensive increase in the consecutive recurrence of the dioestrous 

 cycle, it is not a condition natural to them ; it is due, in all 

 probability, to the care and attention paid to them by man ; in 

 the same way, it may be argued, that the stimulated power 

 of reproduction evinced by certain rodents is also due to the 

 advantages derived from their intimate relations with the 

 luxuries of civilisation (rat and mouse). 



The only animals, so far as is at present known, which 

 experience a continuous series of dioestrous cycles in a state 

 of nature are certain monkeys. 



The fact that it is possible to induce such an enormously 

 increased capacity for oestrus in any animals, prepares one to 

 consider the regular recurrence of the dioestrous cycle in 

 monkeys, and in the human female also, as a very slight step 

 in advance ; and when the whole of the evidence is considered, 



