Development of the Nine-Banded Armadillo. 385 



eight discoid placentae is pressed against the margins of the two 

 contiguous ones so that the whole set forms a ring or zone 

 encircling the vesicle at right angles to the long axis of the uterus. 



The most detailed account of the armadillo placenta yet pub- 

 lished is that of Fernandez, who describes several important early 

 stages of this structure in connection with his account of the early 

 development of the Mulita. 



Chapman ( ; 01), gives a detailed description of the after-birth 

 of a single specimen of Dasypus sexcinctus. Excellent figures of 

 all structures involved accompany the text. As seen from the 

 foetal side the placenta appears to be truly discoidal in form, 

 but on the maternal side the distribution of the villi is decidedly 

 different from that usually found on that type of placenta. The 

 markedly arborescent villi are arranged in a broad, somewhat 

 lobose ring around the margin of the disc, leaving the centre of 

 the latter free of villi, a condition strongly reminding one of a much 

 earlier stage in the development of the placenta of Tatu novem- 

 cinctum, when the original saucer-shaped Trager has begun to 

 produce villi along the free overgrowing margin, but has a com- 

 paratively non-villous central area. The forked connection of 

 the umbilicus with the placenta is almost identical with that found 

 in our species. In view of these striking similarities in the placen- 

 tal details of the two species one is led to conjecture that the con- 

 ditions found in six-banded armadillo closely approximate the 

 ancestral conditions of the more highly specialized armadillos, 

 of which Tatu hybridum seems to be the most pronounced exam- 

 ple and T. novemcinctum the next. 



In view of the fact that there has yet appeared no complete 

 and consecutive account of the history of the placenta of any 

 species of armadillo it seems worth while to devote a special chap- 

 ter to a description of the conditions seen in our species. 



For the earliest condition it will be necessary once more to call 

 attention to the youngest embryonic vesicle of Fernandez. Here 

 we find surrounding the true embryonic layers the trophoblast, 

 which is attached to the uterine mucosa by means of a thickened 

 disc or plug of trophoblast tissue, called the Trager. This attach- 

 ment disc is to be considered as the primary placenta. As the 



JOURNAL OF MORPHOLOGY, VOL. 21, NO. 3. 



