16 MAMMARY APPARATUS OF THE MAMMALIA 



I was able to show that it begins much earlier, 

 in embryos considerably before the time of 

 hatching. 



Fig. 5 is a drawing of Semon's embryo 42, 



ma^ 



hm - 



"am 



~-hm 



-sm 



Fig. 6a.— Echidna: Transvekse Section of Semon's 

 Embryo, showing the Primary- Primordia. 



ma, Primary-primordia ; Am, beginning of the skin muscle. 



in which I noticed the first primordia of the 

 mammary apparatus. I received the embryo 

 cut in transverse sections, and, on examining 

 the slides, I saw that at this stage the forma- 

 tion of hair and spines had not begun ; but 



