Development of the Nine-Banded Armadillo. 391 



In fig. 40 is seen a condition slightly more advanced than that 

 described in detail in our preliminary paper. There is now at 

 each pole of the oval vesicle a star-shaped clear area, with a 

 broad, deeply notched placental zone between, which still shows 

 distinct signs of its origin from four discoid placentae . The notches 

 are more deeply cut along the dorsal and ventral lines than along 

 the lateral, where the placentae of the paired embryos I and II 

 and likewise III and IV are so intimately fused as barely to show 

 the points of union. 



Shortly after the condition just described the placenta takes on 

 what appears to be approximately the definitive condition. The 

 tendency to form two well defined lateral discs is carried still 

 farther, but in no case have we observed the complete separation 

 of the two placental areas. As a rule the bridge between the two 

 main discs is narrower on the dorsal side than on the ventral, but 

 its narrowness is compensated for by the presence of a heavier 

 coating of villi and by that of rather large placental blood-vessels 

 which serve to connect one main disc with the other. It seems 

 to be almost invariably the case that the division into the two dou- 

 ble lateral discs strikes only approximately along the boundary 

 lines of the original discoid areas, for colored injections forced 

 into the placental vessels of individual foetuses run across the 

 narrow placental bridges and invade more or less extensive and 

 clearly marked villous areas of the other main disc. Such a 

 condition is well shown in fig. 41. 



The umbilical cords which may be from 18 to 20 centimeters 

 long are attached rather near the fundus margin of the placentae 

 except in rare -cases where five foetuses occur and involve the 

 crowding of one or more unbilical cords away from the margin. 



Although a litter of young armadillos was born in the laboratory 

 we were not fortunate enough to secure the after-birth and there- 

 fore cannot describe this final stage of the placenta. A comparison 

 of the size and degree of development 1 ^ the new-born young with 

 the oldest foetuses in our possession convinces us that the condi- 

 tions just described stand as definitive. Yet Lane in his recon- 

 struction of the after-birth of the single individual under observa- 

 tion fails to find connecting bridges between the main discs. He 



