Development of the Nine-Banded Armadillo. 395 



Another exceptional condition is that seen in fig. 46, where 

 branching from a typical amniotic canal of one of the embryos, 

 is an accessory c^nal running to an empty amniotic sac at the 

 center of the Trager. Such a condition is doubtless due, as was 

 stated in another place, to the presence of the remains of a degen- 

 erated fifth embryo. Teratological amniotic structures similar to 

 those just described were observed in a number of other cases. 

 In most instances there seems to be no doubt that they represent 

 the retarded or degenerate remains of supernumerary embryos. 

 The frequent occurrence of similar rudimentary embryos in 

 Tatu hybridum and in our own species seems in itself a strong 

 piece of internal evidence of specific polyembryony, for, on the 

 basis of the origin of the several embryos from separate eggs, it 

 would be difficult to understand why some should develop into 

 complete embryos, and others, in the same vesicle and under 

 practically identical conditions, should meet with so little success. 



After the closure of the lumens of the various amniotic canals 

 all communication between the four or more amnia is cut off; 

 and henceforth each embryo has its own separate amnion in as 

 true a sense as in those mammals that produce several entirely 

 independent young. The developmental history of these envel- 

 opes is moreover in no important way different from that of 

 other mammals except that in late stages a gradual fusion occurs, 

 first of all with the wall of the chorionic vesicle and later with one 

 another, where, through the pressure of growth their walls have 

 come into contact. 



Various representative stages in the later history of the amnion 

 are seen in the photographs herewith presented. In fig. 44 

 the amnia may be seen to lie rather closely applied to the bodies 

 of the embryos. In fig. 33 the cavities of the individual amnia 

 have increased greatly in size and the sacs have assumed an ovoid 

 form with the narrower end directed toward the cervix pole of 

 the vesicle. In fig. 34, an external view of the fundus end of a 

 somewhat older vesicle, the amnia are seen pressed against the 

 membraneous area of the Trager, producing at points of contact 

 an added transparency, reminding one of windows through which 

 the embryos can clearly be viewed. 



