226 
CHAS. H. O’DONOGHUE. 
Pregnane}". — (1) A large growth of the mammary gland- 
tissue occurs, due to the mitotic divisions of its epithelial 
cells, and it results in the formation of true alveoli with 
single-layered walls. A substance which resembles milk is 
secreted in small quantities in these alveoli. 
(2) The sebaceous and sweat-glands of the pouch area 
hypertrophy and become active. 
(3) The above changes are very similar to, indeed in- 
distinguishable from, those taking place during pregnancy. 
Stimulus causing the growth of the Mammary 
Glands. — (1) The stimulus causing the hypertrophy of the 
mammary gland at any time is not a nervous one, but of the 
nature of an internal secretion carried by the blood. 
(2) The seat of origin of the stimulus producing this 
growth at puberty, during heat, in virgins that have given 
milk, and in Dasyurus after ovulation not succeeded by 
pregnancy is neither in the foetus nor in the placenta. 
(3) The presence of a functional ovary is necessary for 
the growth of the gland at all times. 
(4) The Corpus luteum is a ductless gland producing an 
internal secretion which is responsible for the attachment 
of the embryo to the wall of the uterus. 
(5) (a) In Dasyurus, in the non-pregnant as well as in 
the pregnant animals, the formation and growth of the 
corpora lutea are intimately connected with the growth of 
the mammary gland. In the non-pregnant animals the 
secretion of the corpora lutea appears to be the only 
assignable cause of the growth of the gland. 
(b) In the rabbit, (a) the presence of an ovary (with 
Corpora lutea) is necessary for the growth of the mammary 
gland; (b) the growth of the mammary gland follows on the 
experimentally induced production of Corpora lutea. 
The general conclusion supported by the above evidence is 
that the Corpus luteum is a ductless gland produc- 
ing a secretion which is the inciting cause of the 
growth of the mammary gland. 
Cause of Milk Secretion. — There is at present no 
