GROWTH-CHANGES IN MAMMARY APPARATUS OE DASYURUS. 225 
(2) The mammary gland anlage arises as a solid cellular 
outgrowth from the follicles of especially strong hairs on the 
primitive teat anlage. 
(3) The hairs on the teat anlage are equal in number to 
the main milk-ducts in the adult teat. 
(4) The proximal solid part of the mammary gland out- 
growth gives rise to the main milk-duct and the distal, 
hollow branches to the mammary tubules of the adult. 
The Adult Gland. — (1) The fully grown gland in 
repose consists of six main ducts, with a lining epithelium 
several cells deep, opening on the teat. The ducts lead down 
into a large number of ramified twisted tubules whose walls 
are two cells thick. 
(2) It is the seat of continuous, but very slow, secretory 
activity. 
Changes prior to Ovulation. — There is an increase in 
the size and activity of both the sebaceous and sweat-glands 
of the pouch area, but very little, if any, growth in the 
mammary gland. 
Changes, during Pregnancy. — (1) There is a large 
increase of mammary gland tissue at this period, resting 
upon the mitotic division of its epithelial cells, and resulting 
in the formation of a great number of true alveoli with single- 
layered walls and a secretion of lymph. 
(2) The sebaceous and sweat-glands of the pouch area 
also hypertrophy and become active, the secretion of the 
latter appearing as drops of a reddish fluid. 
(3) The greater part (practically the whole) of the growth 
in actual gland- tissue occurs before the attachment of the 
embryo. 
Changes after Parturition. — (1) The secretion of 
milk does not commence until about twenty-four hours after 
the birth of the young. 
(2) Such secretion results from a purely secretory activity 
of the cells of the glandular epithelium, and is not connected 
with necrobiosis of either cytoplasm or nucleus. 
Changes when Ovulation is not succeeded by 
