Development of Mammary Glands in the Rabbit. 539 



Contrary to the findings of Ancel and Bouin,* we have never discovered 

 any traces of the myometrial gland in the uteri of rabbits which have been 

 operated on as in this series. 



The effect of the formation of the decidual cells on the mammary gland is 

 negative, no growth or glandular development taking place beyond what 

 occurs in normal pseudo-pregnancy (see Table II). 



These experiments, which were confirmed by the subsequent investigations 

 in which the foetuses were removed (see below), show that the maternal 

 placenta is not the source of the stimulus which causes the glandular phase 

 of the mammary gland. 



The Foetus. 



Lane-Claypon and Starlingf thought that the growth of the mammary gland 

 in rabbits was probably due to the presence of the foetus, and other investi- 

 gators have confirmed their results. Although the actual results of their 

 experiments have been rendered doubtful through the discovery of the action 

 of the corpus luteum, it has not been shown that the foetus is without effect 

 on the mammary gland during the second half of pregnancy. 



Experiments were therefore undertaken to determine the effect of removal 

 of the foetuses from pregnant rabbits, leaving the rest of the generative tract 

 — ovaries, uterus, and placentae — intact. 



WeymeerschJ has shown that the placenta persists in the uterus for some 

 time after the embryo has been removed. Also observation of the placentae 

 of foetuses which had atrophied at an early stage during development 

 showed§ that once started the placentas may persist during the whole course 

 of gestation independently of the attachment of the living foetus. 



The foetuses have been removed from pregnant rabbits between the 13th 

 and 15th days. An incision was made through the uterus and foetal 

 membranes, and the foetus withdrawn by cutting through the umbilical 

 cord. In each case the removal resulted in the arrest of the growth of the 

 mammary gland, and was followed shortly afterwards by the secretion of 

 milk. 



The details of these experiments are given below : — 



Eabbit 1. — Foetuses (3 and 4) removed on the 13th day after coitus. Milk 

 expressed from nipples on the 20th day. Killed on the 25th day. Placenta 

 still attached to the uterine wall, but showing signs of atrophy. Mammary 

 gland not thickened. 



* Ancel and Bouin, ' Compt. rend. Soc. Biol.,' vol. 72 (1912). 



+ Lane-Claypon and Starling, ' Roy. Soc. Proc.,' B, vol. 87 (1906). 



X Weymeersch, ' Ann. Soc. Roy. de Science med. nat. Bruxelles,' vol. 70 (1912). 



§ Hammond, ' Journ. Agric. Sci.,' vol. 6 (1914). 



