410 H. H. Newman and J. T. Patterson. 



4. The fact that all of the embryos of a set are invariably of the 

 same sex strongly suggests their origin from a single fertilized egg. 



5. The definite orientation of the embryos in the vesicle, and 

 of the vesicle in the uterus, precludes the possibility of their origin 

 from several eggs, even though these might conceivably be simul- 

 taneously given off from the ovary. 



6. The inversion of germ layers presents a condition in both 

 Tatu hybridum and in T. novemcinctum, which could not be at- 

 tained by the union of several eggs to form a single vesicle. This 

 is the strongest piece of evidence for specific polyembryony that 

 has been advanced, and, to our minds, is practically conclusive. 



7. The Trager or primitive placenta, common to all four embryos, 

 is the morphological equivalent of that seen in the monembryonic 

 vesicles of certain rodents. 



8. The overgrowing fringe of arborescent villi seen in middle 

 stages of gestation reminds one strongly of the cricoid placenta 

 seen in the monembryonic vesicle of the six-banded armadillo, 

 figured by Chapman. 



9. The existence of partial or rudimentary embryos is evidence 

 against the idea that the several embryos have been derived from 

 separate eggs, for it is difficult to understand why some should 

 develop perfectly, while others, under the same environmental 

 conditions, should have so little success. 



10. The pairing of embryos points to the origin of each pair 

 from one of the first two blastomeres. 



11. The presence of an accessory chromosome in the male germ 

 cells suggests that the spermatozoon is the sex determiner. On 

 this basis the fertilization of several eggs always by the same kind 

 of spermatozoa seems highly improbable. 



