392 H. H. Newman and J. T. Patterson. 



may have observed a rare case in which the line of separation into 

 lateral discs passes exactly between the placental areas of the two 

 dorsal and the two ventral embryos. Moreover we find no such 

 clearly marked non-villous areas at the two poles as he describes. 

 The smooth area at the cervix end is in all of our specimens very 

 small and circular in outline, while that at the fundus end is 

 only vaguely outlined and frequently shows patches of flat 

 villi. 



Any attempt to classify a placenta with the above history 

 meets with grave difficulties, as one might conjecture from the 

 multiplicity of terms applied to it by different writers. Kolliker 

 in his original description of the conditions of the embryonic 

 membranes of T. novemcinctum refers to the placenta as disc- 

 oidal and deciduafce. Milne-Edwards considers it to be com- 

 pound zonary in structure. Beddard describes it as dome-shaped 

 and deciduate; while Lane suggests the term " zono-discoidalis 

 indistincta," subdividing StrahFs class " zono-discoidalis " into 

 two varieties, "distincta and "indistincta." 



Somewhat similar placental conditions, as found inT. hybridum, 

 are designated by von Jhering as indications of a "placenta annu- 

 laris composita." Chapman's use of the term " deciduate cricoid" 

 appears to be apt for the placenta of the six-banded armadillo. 



Of all these terms the one that appeals most strongly as des- 

 criptive of a certain rather persistent phase in the development 

 of this multiformed structure is that used by von Thering, " plac- 

 enta annularis composita," but one must not forget that at first 

 it is simply discoidal, then cricoid, then tetra-discoidal, later 

 annularis composita, and finally incompletely doubly discoidal. 



If animals are to be classified according to the form of their 

 placentae, a method 0f classification that is fortunately falling into 

 disrepute, it would be very difficult to classify the nine-banded 

 armadillo, unless we arbitrarily decide to select some particular 

 developmental phase of the placenta as a criterion for classifi- 

 cation. In such cases one would be led to chose either the primary 

 or the definitive condition and would thus call the placenta either 

 "simply discoidal" or "incompletely doubly discoidal." Other 

 terms scarcely find a rational basis. 



