2 WALTER HEAPIi. 



breediug season have been noted by zoologists, but tlie 

 changes wliicli take place in tlie female generative system 

 prior to gestation require examination which it is impossible 

 to extend, with few exceptions, to mammals in the wild 

 state, and almost all that is known on this matter is derived 

 from a study of domesticated mammals and of some fcAV wild 

 animals kept in captivity. But little attention, however, has 

 been paid to the subject at all by scientific students, while the 

 only attempt, so far as I am aware, which has been made to 

 treat it from a comparative point of view is that of Wiltshire, 

 whose ''Lectures on the Comparative Physiology of Menstrua- 

 tion" were published in the 'British Medical Journal' (1883). 



The subject is of importance in proportion to the light it 

 may throw upon the evolution of the functional phenomena 

 of breeding. To attack such a subject by means of data 

 obtained from the highest groups of animals may seem to 

 many to be beginning at the wrong end of the story, and 

 there is, of course, much truth in that view ; but knowledge of 

 the physiology of the lower animals is at present very limited, 

 and information regarding the habits of most of them at 

 times of reproduction extremely scanty ;^ on the other hand, 

 we have available some knowledge of the habits of many 

 classes of mammals and of the variety of sexual phenomena 

 exhibited by them. 



The data for a comprehensive comparative account even in 

 mammals does not exist; at the same time there is sufficient 

 material at hand, in my opinion, to permit of a foundation 

 being laid, upon which it will be more easy to arrange facts 

 in the future. It is, therefore, not with any idea of finality, 

 but with the purpose of suggesting a wide field of inquiry, 

 and with the hope of assisting therein, that this chapter on the 

 comparative physiology of breeding has been written. 



In the first place, with regard to the terms to be used ; at 

 present there is great confusion regarding those used by 

 breeders ; the same terms are used for both male and female 



^ In this relatiou Dr. Lo Blanco's papers in the ' Miith, Zool. Stat. 

 Neapel,' vol. viii. 1888, and vol. xiii, 1899, are of great value. 



