THE CESTROUS CYCLE IN THE MAMMALIA 53 



not been successful, or when the animals were not permitted to breed. 

 If allowed to become pregnant the lioness at Dublin may still experi- 

 ence two sexual seasons, and have two litters of cubs within the 

 year. Thepuma in the Dublin Gardens is stated to have one sexual 

 season annually if breeding, or two if there is no gestation. The 

 larger Felidae as a rule breed comparatively freely in confinement, 

 some places, such as the Dublin Gardens, being famous for successful 

 lion breeding. The period of gestation in the lioness is from fifteen 

 to sixteen weeks ; . that of the tigress is about twenty-two weeks ; 

 while the puma goes with young for fifteen weeks. 



Most species of bears, both in their w9& state and in confinement, 

 are monoestrous and have one annual sexual season. The grizzly 

 bear, however, according to Somerset,^ bears young only once in two 

 years. The bears in the Zoological Gardens at Dublin, on the other 

 hand, may experience more than one annual sexual season if 

 pregnancy does not occur. The period of gestation in the brown 

 bear is seven months; in the grizzly bear it is probably longer. 

 Heape states that with the bears in the Zoological Gardens in 

 London oestrus may be experienced for two or three months 

 continuously ; but this condition, as he points out, is unnatural and 

 probably an effect of confinement, for though coition can occur, it 

 does not, as a rule, result in pregnancy. 



The ferret, which is a domesticated variety of the polecat, is 

 monoestrous, but may have as many as three annual sexual seasons,^ 

 .which, however, instead of being distributed at regulair intervals 

 throughout the year, occur only in the spring and summer, the 

 autumn and winter being occupied usually by a prolonged ancestrous 

 period.® This tendency towards a concentration of sexual seasons 

 during one part of the year may be considered as an approach to a 

 condition of polyoestrum ; for, if the oestrous periods were to recur 

 at still shorter intervals than is actually the case, they could be 

 regarded as forming so many dioestrous cycles in one sexual season. 

 So far as I am aware, the ferret does not experience oestrus more 

 than twice annually if allowed to breed. 



The polecat is also monoestrous, but breeds only once a year. 

 Mr. Cocks informs me that in captivity the young of this animal are 

 generally born in the first half of Jane, and that the gestation peiiod, 

 as in the ferret, is about forty days. 



The stoat, weasel, and pine- marten, in their wild state, are almost 



1 Somerset. Quoted by Heape, loc. cit. ^ 



2 Carnegie, Ferrets and Ferreting, London. 



3 Eobinson (' ' The Formation, Rupture, and Closure of Ovarian Follicles in 

 Ferrets etc.," Trans. Roy. Soc. Edin., vol. lii., 1918) finds that the size of the 

 ovary varies at different periods. It is smallest in the ancestrum and largest 

 about mid-pregnancy. At cestrus it is intermediate. 



