372 THE PHYSIOLOGY OF REPRODUCTION 



of the myometrial gland (see below, p. 618), but Hammond 1 has 

 shown that it is far more likely to be due to the continued influence of 

 the corpora lutea, depending upon the presence of the foetus, since 

 these organs do not attain the same dimensions under the experi- 

 mental condition (which may be called pseudo-pregnancy, a condition 

 not normally occurring in the rabbit, which usually only has corpora 

 lutea associated with pregnancy, since it does not ovulate without 

 copulation). According to Hammond, the corpora lutea do not 

 degenerate in the later part of pregnancy, and consequently the 

 corpora lutea of pseudo-pregnancy in the rabbit are comparable to 

 the corpora lutea spuria of most other Mammals, although it would 

 seem probable that, when produced, they persist for a longer time 

 and exert a greater influence than the " false " corpora lutea of those 

 polyo3strous animals which ovulate spontaneously. Milk may be 

 expressed from the glands towards the end of the pseudo-pregnant 

 period even in rabbits which have only copulated once, having 

 previously been virgins. The uterine hypertrophy occurring under 

 the influence of the corpus luteum formed after sterile coition has 

 been shown to be very pronounced in the rabbit, while the blood 

 extravasation towards the end of pseudo-pregnancy is also marked 2 

 (see above, p. 101). 



Lastly, it has been found that rabbits which had been pseudo- 

 pregnant will pluck their breasts and prepare a nest for young 

 although there were none to be born (see below, p. 576). 



In the marsupial cat (Dasyurus) there is only one kind of corpus 

 luteum 3 (that of pregnancy or pseudo-pregnancy), and the changes 

 which occur in the mammary glands as a result of luteal influence 

 are identical irrespectively of whether gestation occurs or not. The 

 uterine changes are in a general way similar to those occurring under 

 artificial pseudo-pregnancy in the rabbit. 4 



Leo Loeb 5 has shown that in the non-pregnant giiinea-pig there 

 is a definite cycle for the mammary gland and that it corresponds 

 with the ovarian and uterine cycles. The gland tissue proliferates 

 when a new ovulation is imminent and to a greater extent later in 

 the cycle as a result probably of the cumulative influence of the 



1 Hammond, " On the Causes Responsible for the Developmental Progress 

 of the Mammary Glands, etc.," Proc. Roy. Soc., B., vol. Ixxxix., 1916. 



2 Hammond and Marshall, "The Functional Correlation between the 

 Ovaries, Uterus, and Mammary Glands," Proc. Roy. Soc., B., vol. Ixxxvii., 1914. 



3 Hill and O'Donoghue, "The Reproductive Cycle in the Marsupial Dasyurus," 

 Quar. Jour. Micr. Science, vol. lix., 1913. 



4 Retterer and Voronoff (C. R. de la Soc. de Biol., vol. Ixxxiv., 1921) record 

 growth of uterine glands and cotyledons in goats and sheep through an ovarian 

 graft containing a corpus luteum and after previous ovariotomy. 



5 Loeb and Hesselberg, " The Cyclic Changes in the Mammary Gland under 

 Normal and Pathological Conditions," Jour, of Exp. Med., vol. xxv., 1917 ; see 

 also Biol. Bull., vol. xxvii., 1914. 



