THE "sexual season OF MAMMALS. 11 



tilised; gestation results and persists until parturition takes 

 place. 



After parturition there may be a considerable interval of 

 rest ; this interval may occupy only what remains of the 

 anoestrous period which the same animal would experience 

 in case it had not borne young, or it may persist during a 

 nursing period which extends beyond the normal limits of 

 such anoestrous period, or it may be even still further pro- 

 longed. On the other hand, parturition may be followed 

 almost immediately, and in spite of the nursing period, by 

 pro-oestrum, oestrus, insemination, and renewed gestation. 

 While finally, the same animal may at one time of the year 

 exhibit a recurrent gestation, Avhile at another time of the 

 year its generative organs may continue fallow for the re- 

 mainder of that interval which represents the anoestrous 

 period. 



Such briefly are the different types of breeding' phenomena 

 exhibited by female mammals during their reproductive 

 period; the following account will show that they all con- 

 form to one plan, and that the variabilit}^, which altered 

 conditions of life induce therein, clearly indicates the origin 

 of these types. On this account the subject is likely to be 

 of considerable interest to students of variation, and the 

 collection of facts which bear thereon is urgently needed. 



The Sexual Season of Male Mammals. 



It is unnecessary to do more than mention here that males 

 may be divided into two classes : those which rut (stag), and 

 those which do not rut (dog). Eutting males have a special 

 sexual season; those which do not rut experience sexual 

 capability all the year round. 



The sexual season of some males in captivity ^ is capable 



1 Information regarding wild animals in captivity, unless otlierwi&e stated, 

 has been obtained from certain keepers in tlie Zoolon:ical Gardens of London, 

 whose statements appear to me to be reliable. The reference given in the 

 text is (Zoo.). 



