DEVELOPMENT IN WDELPHYS 



71 



epidermis. In the stage 3-8 centimetres long, 

 corresponding to the dark tones in Fig. 22, 

 there are now present on either side of the 

 nipple primordia well-marked ingrowths of 



Fig. 25. — Transverse Section of Abdominal Skin 

 IN THE Region of the Nipple Primordia of 

 "didelphys marsupialis." successive stages. 

 (Bresslau.) 



the epidermis. These then extend inwards so 

 rapidly that at the stage 4*4 centimetres they 

 are much larger than the nipple primordia, 

 and, as a sectional reconstruction shows, they 

 surround the latter in the form of continuous 



