6i8 THE PHYSIOLOGY OF REPRODUCTION 



about the eighteenth day the rabbit may display the instincts 

 associated with parturition (see p. 576). In true pregnancy the milk 

 glands still continue to grow, increasing in thickness and in weight 

 until from the twenty-fourth to the thirtieth day, that is to say, 

 untU at or near the time of parturition.'^ The pseudo-pregnant 

 condition thus differs from that of true pregnancy. Similarly in 

 the pseudo-pregnant bitch the milk glands do not hypertrophy to 

 the same extent as in the pregnant animal. In both species of 

 Mammals the differences in mammary development are less marked 

 in individuals which have previously borne young and in which 

 consequently the mammary glands had already undergone a hyper- 

 trophy which was to a great extent persistent. 



Ancel and Bouin ^ ascribe the growth of the milk glands in the 

 later part of pregnancy to the rayometrial gland, which is stated to 

 consist of clumps of epithelioid cells lying under the placental cells 

 and between the muscle cells of the longitudinal and circular coats 

 in close proximity to the blood-vessels. They suggest that this 

 gland is an organ of internal secr.etion which takes over the functions 

 of the corpus luteum during the second half of pregnancy, controlling 

 the later or " glandular " phase of the mammary gland as well as the 

 tolerance of the uterus for the foetus. Fraenkel ^ has confirmed the 

 observations upon the presence of the myometrial gland in the rabbit 

 but has failed to find it in other species examined. Mercier,* 

 however, has identified the cells of the gland with certain phagocytic 

 cells which he had previously found in the pregnant uterus. 

 Hammond^ says that they are not constant even in rabbits, and 

 when present are probably foetal cells which have wandered into 

 the muscular coat. 



As already mentioned, the placenta has also been suggested as a 

 source of the stimulus for the mammary growth of pregnancy. 

 Hammond, however, has eliminated this organ as a possible factor 

 by causing decidual tissue to form through the stimulation of the 

 uterus by a foreign body or by an incision after the manner of Loeb 



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

 of the Mammary Glands in the Rabbit in the latter part of Pregnancy," Froc. 

 Roy. Soc, B., vol. Ixxxix., 1917. 



2 Ancel and Bouin, " Sur TExistence d'un Glande Myom6triale, etc.," ' 

 C. R. Assoc, des Anat., 13 Reunion, 1911; "Recherches sur les Fonctions 

 du Corps jaune gestatif," Jour, de Phys. et de Path. Oen., vol. xiii., 1911; 

 " Sur I'Evolution de la Glande mammaire pendant la Gestation," C. R. de la 

 Soc. Biol., vol. Ixxii., 1912. See also C. li. de I'Acad. des Sciences, vol. cliv., 1912. 



3 Fraenkel, " Untersuchungen iiber die Sogenannte Glande endocrine 

 myom6triale," Arch. f. Oyn., vol. xcix., 1913. 



* Mercier, "Sur I'Existence de Nephrophagocytes dans le Muscleuterin, 

 etc.," G. R. de la Soc. de Biol., vol. Ixxii. ; and other papers in vols. Ixxiii. and 

 Ixxiv., 1912 and 1913. 



5 Hammond, loc, dt. 



