Development of Mammary Glands in the Rabbit. 545 



of development of the gland in the pregnant and the pseudo-pregnant 

 condition is quite distinct. 



Table II shows the results obtained. Comparing this with Table I it is 

 seen that there is a definite correlation between the development of the 

 corpus luteum and the increase in weight of the mammary gland. 



Summary and Conclusions. 



1. Experimental results show that the development of the mammary 

 gland of the rabbit during the second half of pregnancy is under the same 

 influence as that which controls the development during the first half, 

 namely, the corpus luteum. 



2. Contrary to the generally accepted opinion, this gland (the corpus 

 luteum) is active during the second half of pregnancy. 



3. The further development of the corpus luteum, which takes place during 

 the latter part of pregnancy, is due to the influence of the foetus. 



4. The experiments do not uphold the view of Ancel and Bouin that the 

 glandular phase of the mammary gland is due to something entirely different 

 from that which causes the growth-changes, but confirm the views expressed 

 in an earlier paper by Hammond and Marshall, in which it was shown that 

 milk secretion in pseudo-pregnancy takes place in correlation with the 

 involution of the corpus luteum. 



Apparently the secretion of milk results whenever the influence causing 

 the glandular growth (the corpus luteum) is removed or lessened in amount, 

 provided that the initial development has gone far enough. 



The experiments described above were performed in 1913-14 at the 

 School of Agriculture and Field Laboratories, Milton Eoad, Cambridge. The 

 expenses were, for the most part, defrayed by a research grant from the 

 Board of Agriculture and Fisheries out of funds placed at their disposal by 

 the Development Commissioners. 



I am greatly indebted to Dr. F. H. A. Marshall for the help he has given 

 me in preparing this paper. 



