DEVELOPMENT IN DIDELPHY8 73 



caudal pairs of nipple primordia are clearly seen. 

 Round the central primordium and the fourth 

 pair, however, they are only beginning to 

 develop. These primordia obviously belong to 

 the inner series of the four-rowed arrangement 

 that we have already recognized. I would 



Fig. 27. — Abdominal Wall of Young Didelphys, 

 (Bresslau.) 



Micro-photograph, 12 diameters. 



especially emphasize that these ring-shaped 

 ingrowths are to be regarded as individual 

 formations, and as a proof of this, one can see 

 in the figure that their lateral walls form dis- 

 tinct convex projections. 



But this condition does not last long. In 

 young only slightly larger than the last stage 



