Ovaries, Uterus, and Mammary Glands in Rabbit. 433 



pregnancy in association with the development of the embryo, whose 

 presence necessitates the maintenance of a raised nutrition on the part of 

 the organ which protects it and through which it derives nourishment. 

 That the corpora lutea are a factor in preserving this raised nutrition 

 seems to have been established beyond question. 



The (Estrous Cycle. 



According to Heape a period of five or six months (i.e. spring and summer) 

 is the usual duration of the sexual season in the domesticated rabbit. 

 Heape says further : " No doubt if they are kept warm, carefully fed, and 

 their breeding carefully regulated throughout the spring and summer, they 

 may exhibit oestrus also in winter, but it must be recollected that here 

 we are treating of oestrus independently of pregnancy, which is a very 

 different matter." 



Our experience has been different from that of Heape, for many of our 

 rabbits, kept in hutches in an outhouse and without any artificial heating, 

 have bred in the winter months, though not with the same frequency as 

 in spring and summer. The following is a record : — 





Percentage 

 breeding. 



„ 24 „ „ Mar. 22, 14 „ 



„ 21 „ „ May 18,17 „ 



41-7 

 58 -3 

 81 -0 

 100 -o 



Half of these rabbits had been treated with Yohimbine, administered by 

 the mouth for several days before copulation, but the drug, although in 

 other cases it caused a pronounced congestion of the uterus, did not 

 increase the breeding powers or affect the fecundity, as compared with the 

 other rabbits which were kept as controls. 



Prof. Punnett, who has kindly supplied us with further information con- 

 cerning the recurrence of oestrus in rabbits, finds that when kept in a 

 moderate temperature, produced when necessary by artificial heating, not 

 only is there very little, if any, restriction of the sexual season to a 

 particular time of the year, but that copulation in the winter is followed 

 by pregnancy. The following is a record of the oestrous periods (so far as 

 observed) and times of litters for one of Prof. Punnett's rabbits from 

 October, 1910, to May, 1912:— 



