THE CORPUS LUTEUM 733 



glands is produced. It is hard to see why if the ovary may be 

 effective at one time it should not also be effective at another. 



Several authors have pointed out that the removal of both 

 ovaries before puberty prevents its onset with the accompanying 

 growth of the mammary glands. It is well known too that there 

 is a growth of these glands at puberty and again at each cestral 

 period. In connection with the latter an interesting case has 

 been cited of a woman with supernumerary mammary glands 

 which not only enlarge but actually secrete milk at each cestral 

 period. All these enlargements of course synchronise with 

 periods of ovarian activity which include ovulation and the 

 formation of corpora lutea. 



In the course of their experiments Lane-Claypon and Starling 

 noted that if the ovaries and uteri were removed from a rabbit 

 before the fourteenth day of pregnancy the mammary glands 

 return to a state of rest without giving milk. If the same 

 operation were performed after that time milk was expressible 

 within two days, that is to say, the glands had reached a stage 

 of development at which they could become functionally active. 

 But the corpora lutea have also reached their maximum growth 

 by the fourteenth day and after that time begin to diminish. 



All these points, considered in the light of what is already 

 known of the connection between the uterine changes and the 

 corpora lutea, suggest the probability of a relation between these 

 bodies and the mammary glands. 



Turning now to consider the condition in the Marsupial, 

 Dasyurus viverrimis, we find that the adult resting gland 

 consists of six main ducts lined with an epidermis four or five 

 cells thick. Some distance below the epidermis each duct 

 breaks up into a number of branching tubules, lined with an 

 epidermis two cells thick. The growth of the gland falls into 

 two distinct phases. Firstly, the stage of actual formative 

 growth during which the glandular cells lining the mammary 

 tubules increase rapidly by mitotic division and in which the 

 total number of cells is increased many times. As a result of 

 this growth the mammary tubules become much more ramified 

 and throughout their length hollow bud-like outgrowths, the 

 primitive alveoli, are formed. Towards the end of this period 

 the lumina of the tubules and their outgrowths begin to enlarge 

 and the cells lining them begin to arrange themselves in a single 

 layer. Secondly, a stage of enlargement, during which the 



