54 THE PHYSIOLOGY OF REPRODUCTION 



certainly mon<iestrous and breed once a year. In the last-mentioned 

 animal Cocks l found that a single oastrus may last a fortnight. The 

 stoat and weasel do not appear to have been bred in captivity. The 

 otter in a state of nature breeds only once a twelvemonth (in winter, 

 as a rule, but young may be born at any season according to Cocks). 

 In captivity, however, oestrus may recur at regular monthly intervals 

 all the year round. 2 



The various species of seals are in all probability moncestrous, 

 and have one litter of young annually. Some species show an almost 

 perfect rhythmic regularity in the recurrence of their breeding 

 season. Thus, in the case of the harp seal in the north-east of 

 Newfoundland, and also in Greenland, according to Millais, 3 the pups 

 are born each year between 8th and 10th March. Farther north, 

 however, at Jan Mayen, they are not born until about 23rd or 24th 

 March. Turner's notes 4 on the breeding habits of seals also point to 

 the conclusion that the sexual season with these animals is restricted 

 to" regular periods of comparatively short duration, so that it may 

 probably be assumed that seals are monoestrous. The males of 

 seals, as already remarked, experience rut at the time of the female 

 sexual season. Whether the male generative organs are functional 

 (e.g. whether the testes produce sperms) at other times does not 

 appear to be known. It is of interest to note that in many species 

 the rut is experienced during a period of complete fasting. Thus it 

 is stated that the male fur seal, after coming to land, may live for 

 over a hundred days without taking food, and that during this period 

 he is constantly engaged in struggles with other males, finally 

 leaving the shore in a state of extreme emaciation. 



The walrus affords an example of a mammal which bears young 

 only once in three years. Parturition takes place about May or 

 June, and the sexual season recurs about two years subsequently. 



1 Cocks, "Note on the Gestation of the Pine-Marten," Proc. Zool. Soc., 

 1900. 



2 Cocks, "Note on the Breeding of the Otter," Proc. Zool. 8oc., 1881. 

 Mr. Cocks' subsequent experience, concerning which he has been kind enough 

 to write to me, confirms the conclusion that there is no anoestrous period in 

 the otter in captivity. There has been some controversy regarding the 

 breeding of the badger. According to Meade- Waldo the period of gestation 

 is between four and five months (" The Badger: its Period of Gestation," 

 Zoologist, 1894), but according to Cocks ("The Gestation of the Badger," 

 Zoologist, 1903, 1904), this period may be anything between under live and 

 over fifteen months, for although the sexual season may apparently occur at 

 any time of the year, the young are invariably born within a period limited 

 to six weeks. This extraordinary conclusion is based on a number of observa- 

 tions. Fries ("Tiber die Fortpflanzung von Mvd.-s tii.m.s," Zool. Anz., vol. iii., 

 1880) describes the badger's ovum as undergoing a resting state during which 

 development is at a standstifl (cf. roe-deer, p. 43). 



3 Millais, loc. cit. 



4 Turner, "On the Placentation of Seals," Trans. Roy. Soc. Edin., vol. 

 xxvii., 1875. 



