200 



J. A. MYERS 



The time of formation of the lumen evidently is subject to 

 considerable variation. While its first appearance was observed 

 in eighteen day and nine hour and nineteen day and six hour 





ep. m. 



Fig 3 Drawn from a section through right first thoracic developing mam- 

 mary gland of a female albino rat fetus of twenty days and six hours. X 3C0. 

 Zenker's fixation; hematoxylin-eosin stain. Drawn with the aid of a camera 

 lucida. c, irregularly arranged developing connective tissue cells ■,c.t., deve op- 

 ing connective tissue forming sheath around duct ; ep.in., epithelial ingrowth or 

 hood; n.a., nipple anlage; p.d., primary duct ; .s., sulcus surrounding nipple anlage. 



