PLATE 4 



EXPLANATION OF FIGURp:S 



Lettering for figures 14 to 17 as follows: ep.in., epithelial ingrowth of the nip- 

 ple; /)./., hair follicle; l.d., lactiferous (primary) duct; m., muscle; n.a., nipple 

 area; s, sulcus at base of nipple. 



14 Drawn from a section through the nipple area of the second inguinal gland 

 of a newborn albino rat. X 67. 



15 Drawn from a section through the nipple area of the second inguinal gland 

 of an albino rat one week old. X 67. 



16 F'rom a section through the nipple area of the second inguinal gland of an 

 albino rat two weeks old. X 67. 



17 From a section through the ni])ple of the second inguinal gland of an albino 

 rat nine weeks old. X 67. 



388 



