412 J. A. MYERS 
somewhat medial to the abdominal and inguinal nipples. Just 
under the nipple and partially occupying the epithelial hood is a 
condensed mass of fibrous tissue which becomes continuous with 
the less dense fibrous tissue of the nipple. Deep to and sur- 
rounding this mass of tissue is the loose stroma of the gland. 
During this stage the blood-vessels in the stroma become 
enlarged so that in fresh specimens one notices a considerable 
increase in the vascularity of the gland as compared with the 
preceding stages. 
As in the six weeks’ stage, the primary duct in the male does 
not communicate with the exterior on account of a short solid 
cord of cells existing between its lumen and the very shallow 
lumen of the intra-epidermal duct. Moreover, it has been pointed 
out Myers (717 b) that the marked growth of the female gland at 
the time of puberty does not usually occur in the male. The 
terminal enlargements appear similar to those in females of six 
and seven weeks. The walls of the ducts are composed of two 
layers of cells with the same arrangement as in the female. 
However, observations have revealed no indication of lobulation 
or developing alveoli in the male. 
DISCUSSION AND CONCLUSIONS 
In the following discussion, the nipple, the epithelial hood, 
milk-ducts, secretion in the new-born, and gland stroma will be 
successively considered. 
The nipple pocket and epithelial hood 
It will be recalled that in female fetuses of twenty days and six 
hours the nipple appears as a small elevation lying at the bottom 
of the mammary pit (Myers, 717). After the twenty days and 
six hours’ stage the nipple grows so that at the time of birth in 
the female albino rat it nearly fills the mammary pit and appears 
as a somewhat round light area lying at the same level or very 
slightly elevated above the surrounding epidermis. At the end of 
the first week of postnatal life (fig. 12) the nipple is only a little 
more elevated than in the new-born. During the second week 
