DEVELOPMENT OF NIPPLES 63 



In spite of the fact that the piece of skin 

 had to be stretched out flat in order to obtain 

 this preparation and so pulled out of shape, 

 you can gather from the figure how far 

 originally the primary-primordia extended, and 

 how each of the elongated oval primary areas 



Fig. 22. — Abdominal Wall of Young Didelphys. 



fBRESSLAU.) 

 Micro-photograph 18 diameters. 



has produced one of the primordia of the central 

 pair. Observe now in Fig. 21, taken at a 

 magnification of twelve diameters, how far the 

 lateral rows of nipple primordia are separated 

 from each other, and compare with this Fig. 22 

 of a young one, 3-65 centimetres long, taken 

 at a magnification of eighteen diameters. In 



