18 MAMMARY APPARATUS OF THE MAMMALIA 



bloodvessels (Fig. 6c). Internally to the cutis 

 the beginnings of the trunk muscles were 

 distinctly seen. Further, the primordia of the 

 skin muscle were visible as thickenings of the 

 cutis, which extended ventrally on either side 

 as far as the epidermal thickenings. 



These formations undoubtedly represent the 

 first primordia of the mammary apparatus, the 



Fig. 6c. — Echidna: Semon's Embryo. Transverse 

 Section through the Primary-Primordia, show- 

 ing THE Epidermal Thickening and the Under- 

 lying Condensed Tissue of the Dermis. 



primary-priniordia as I call them. It occurred 

 to me that they must have been visible in the 

 entire embryo. This supposition admitted 

 of positive proof, thanks to the care with 

 which Semon had his material illustrated. 

 If you look at the drawing (Fig. 5) you will 

 see on the right side of the trunk a white 

 spot (ma), which exactly corresponds to the 



