Development of the Nine-Banded Armadillo. 361 



were not appreciated. To him however belongs the credit of 

 having discovered specific polyembiyony in the Mulita. 



No attempt was made to secure evidence, either internal or 

 external, of the validity of von Jhering's suggestion until Rosner, 

 ('01), took up the subject in connection with his studies of human 

 monochorial twins. On the basis of a histological examination 

 of the ovaries of one pregnant female of the South American nine- 

 banded armadillo he attempted completely to discredit the idea 

 that the several embryos of a litter arise from a single fertilized 

 ovum. Since his observations strike at the very foundations of 

 the question of polyembryony in the armadillos it seems neces- 

 sary to review his work in some detail. 



The genitalia of two pregnant females were sent to him by 

 von Jhering, and an examination showed that the ovaries of only 

 one specimen were sufficiently well preserved to admit of histo- 

 logical examination. Sections of the other pair of ovaries showed 

 that a large percentage of follicles contained more than one egg. 

 There were in all 52 large follicles : 1 1 with 2 eggs, 7 with 3, 2 with 

 4, 1 with 5, and 1 with 7. The two largest follicles contained four 

 eggs, exactly the number necessary to produce the four embryos 

 habitually brought forth in a litter of this species. Since the 

 youngest follicles never contained more than one egg the condi- 

 tions seen in the older ones must have resulted from secondary 

 fusions of adjacent follicular walls, which subsequently disap- 

 peared in such a way as to form a common cavity. The author's 

 figures are evidently accurate representations of actual observa- 

 tions and are calculated to convince the reader. Especially strik- 

 ing is the figure of a reconstruction of a series of sections through 

 a large pluriovular follicle in which each of the eggs has its own 

 thick coating of discus proligerus cells. 



Rosner believes that the observed condition of four embryos 

 surrounded by a common chorion is to be explained by the fol- 

 lowing sequence of events: four adjacent follicles fuse in such a 

 way that four eggs are thrown into a single cavity ; on the rupture 

 of this compound follicle the four eggs are discharged simultan- 

 eously, descend the fallopian tube held together in a mass by 

 means of their discus proligerus cells, become fertilized, undergo 



