56 THE PHYSIOLOGY OF REPRODUCTION 



to a tendency on the part of the Dublin specimens to adapt 

 themselves to the climatic conditions of Ireland. At the same 

 time it should be mentioned that certain indications were ob- 

 served in connection with the demeanour of the parents towards 

 each other which seemed to indicate that the sexual instinct 

 was excited at more than one period of the year." The period 

 of gestation was ascertained to be about eighty days, or nearly 

 three weeks longer than in the domestic dog. " As might be ex- 

 pected, the young when they are born are more lusty and more 

 advanced in development than new-born puppies of the dog." 

 On one occasion, when the litter produced was unusually large, 

 the gestation period was lengthened to eighty-six days. 1 



The female of the domestic cat generally breeds two or 

 three times a year. According to Spallanzani 2 the " heat " 

 periods occur in February, June, and October, but there can 

 be no doubt that many individuals breed at other times, and 

 that there is great variation. 3 Heape 4 says that there may be 

 no less than four sexual seasons within a year, but this can 

 only be when the cats are not allowed to become pregnant. 

 The usual number of litters, in my experience, is two, in typical 

 cases in spring and autumn as in the dog. Heape states also 

 that feral cats breed only once a year. The domestic cat is 

 polyoestrous, and may experience a long succession of dioestrous 

 cycles in one sexual season, each dioestrous cycle lasting about 

 fourteen days and sometimes less. 5 The period of gestation is 

 about nine weeks. 



Millais 6 says it is uncertain whether the wild cat has one 



1 Cunningham (D. J.), " Cape Hunting Dogs (Lycaon pictus) in the Gardens 

 of the Royal Zoological Society of Ireland," Proc. Roy. Soc. Edin., vol. xxv., 

 1905. 



2 Spallanzani, Dissertations, vol. ii., London, 1784. 



3 Marshall and Jolly, lc. cit. I have known a cat experience oestrus 

 regularly at intervals of about a fortnight from December until the following 

 August, but such a long succession of dioestrous cycles is probably unusual. 



4 Heape, loc. cit. 



s Heape, loc. eit. Mr. W. O. Backhouse informs me that in his experience 

 with Siamese cats the females, if the kittens are destroyed or birth is 

 premature, come on heat regularly about eight days after parturition. This 

 probably occurs in other breeds, at any rate in spring and summer. 



8 I am much indebted to Mr. A. H. Cocks for supplying me with interest- 

 ing information concerning various Carnivora in captivity. 



