TWINNING IN DASYPUS NOVEMCINCTUS 65 



to one large lateral disk and one fetus to a smaller disk 

 on the opposite side. Again, in two sets (Figs. 21 and 

 22) that are in approximately the stage shown in Fig. 19, 

 an interesting irregularity appears in the arrangement 

 of the amniotic connecting canals with reference to the 

 common amnion. Instead of having the usual dicot- 

 omous branching on each side, there are in both cases 

 three connections on one side and a single unbranched 



Fig. 21 



Fig. 22 



Figs. 21 and 22. — Outline views of the common amnion and the 

 connecting canals of fetuses. These were drawn from two eggs that 

 were in stages between Figs. 18 and 19. In Fig. 21 the canal of fetus II is 

 separated far from its partner, fetus I. In Fig. 22 fetus IV seems to 

 have originated separately and does not seem to be paired with fetus III. 

 These are cases of non-pairing and may represent a not uncommon 

 condition. 



connection on the other. Doubtless if a larger collection 

 of equivalent stages were available other similar con- 

 ditions would be revealed. This departure from the 

 symmetrical paired arrangement is significant when 

 compared with what Fernandez describes for the 

 Mulita, where the irregular condition is the rule and 

 there is little evidence of pairing (compare Figs. 27-31). 



