Development of the Nine-Banded Armadillo. 



389 



a. V. 



-II 



Fig. 3. A semi-diagrammatic representation of a vesicle seen from the dorsal 

 side. II, III, and IV are the placental discs of the embryos so numbered. Note 

 that those belonging to the paired embryos III and IV are closer together than 

 II and III. f.v., flattened villi of the Trager; h., horn of the yolk sac. X 2. 



Fig. 4. A semi-diagrammatic drawing of the dorsal view of a vesicle slightly 

 older than that seen in fig. 3. This shows the fusion of the placental discs I, II, III, 

 and IV into a zone. Note that the fusion between the discs of III and IV (of paired 

 embryos) is more intimate than between II and III. In the cervix region of the 

 vesicle the dorsal part of the overgrowing placental ring, p.r., has been removed 

 to show the smooth yolk-sac lying within (y.*.). The ring was fused with the wall 

 of the cervix at "z". The dotted line lying j ust above the discs represents the line 

 along which the upper part of the ring was cut. X 2. 



The yolk-sac region of the vesicle is from this period on cut off 

 from all contact with the uterine wall except at the mouth of the 

 uterus where a small circular area remains uncovered by any 

 outer layer. This condition persists until birth except that the 

 overgrowing ring of arborescent villi undergoes a gradual degene- 

 ration, as the placental discs increase in functional prominence 

 until the long, branched villi become mere flattened prominences, 

 which serve only to slightly roughen the membraneous area at 

 the cervix end of the vesicle. 



