THE CESTROUS CYCLE IN THE MAMMALIA 51 



in a state of nature, that the lycaon breeds only once a year, and 

 that the irregularity noticeable in the fourth and fifth litters is due 

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

 selves to the climatic conditions of Ireland. At the same time it 

 should be mentioned that certain indications were observed 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 expected, 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 diojstrous cycles in one sexual season, each dicestrous cycle lasting 

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



*/ O 



from fifty-six to sixty-three days. 6 



Millais " says it is uncertain whether the wild cat has one or two 



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

 of the Boyal Zoological Society of Ireland," Proc. Roy. Hoc. Edin., vol. xxv., 

 1905. 



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



3 Marshall and Jolly, Joe. cit. I have known a cat experience cestrus 

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

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



4 Heape, loc. fit. 



5 Heape, loc. cit. 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. 



6 There is some evidence that cats, like rabbits, may experience pseudo- 

 pregnancy after sterile coition, since milk secretion may occur. See p. 131. 

 (Doncaster, "A Possible Connection between Abnormal Sex-Limited Trans- 

 mission and Sterility," Proc. Camb. Phil. *S'oc, vol. xvii., 1914). Barrington 

 shows that the glandular epithelium of Bartholin's glands in cats becomes 

 rich in mucin shortly before <estrus and in the last half of pregnancy. ("The 

 Variations in the Mucin Content of the Bulbo-Urethral Glands," Internal. 

 MonaU&chr. f. Anat. ttnd P/ii/*. t vol. xxx., 1913.) 



7 Millais, loc. cit. I am much indebted to Mr. A. H. Cocks for supplying 

 me with interesting information concerning various Carnivora in captivity. 



