22 WALTEL4 HEAPE. 



recollected tliat without accurate observation^ during- the ab- 

 sence of the male, it cannot positively be asserted that such 

 animals are monoestrous. 



In the case of the bitch, in Danish Greenland the bitch 

 generally experiences only one sexual season per annum, 

 though sometimes she may have two (Rink, 1877). 



In this country, as a rule, the bitch has two sexual seasons 

 each year, one in the spring and one in the autumn, but there 

 are wide variations to this rule. She may have only one 

 sexual season per annum, or it may occur every eleven, ten, 

 nine, eight, seven, six, five, or four months (vStonehenge, 

 1887). It seems probable the sexual season recurs less 

 frequently in breeds of large dogs as a rule; a correspondent 

 (Dr. lumann), who breeds St. Bernard dogs, informs me this 

 is his experience, and I have had information from other 

 breeders of large dogs, mastiffs and bloodhounds, which shows 

 there is an obvious tendency in this direction ; at the same 

 time it does not appear to be by any means a universal rule. 

 Again, while the spring and autumn are the usual times when 

 the sexual seasons of dogs occur, the sexual seasons of each 

 bitch have a more or less exact periodicity peculiar to herself. 

 Finally, the sexual seasons of any bitch may be interfered 

 with to the extent even of complete cessation, if she is sys- 

 tematically prevented from breeding. 



The bitch may be considered a case of extreme variation in 

 the periodicity of the sexual seasons of a moucestrous domes- 

 ticated mammal. The normal two sexual seasons experienced 

 in this country are reduced usually to one in Danish Greenland, 

 probably owing to the effect of climatic influences, while the 

 variations which exist in this country indicate the effect of 

 individual influences, which are largely stimulated by artificial 

 selection and domestication. 



The wolf, jackal, and fox are monoestrous like the dog, and 

 in captivity in the Zoological Gardens they show two sexual 

 seasons per annum, like the normal dog in this country. 



Bears are also monoestrous, but they have only one sexual 

 season per annum in the Zoological Gardens. 



