POLYEMBRYONIC DEVELOPMENT IN TATUSIA 645 



SUMMARY 



The main facts brought out in the descriptive part of the paper 

 may be summarized as follows: 



1. The arrangement of the folds of the uterine mucosa is such 

 that there is formed a distinct cross-shaped area of compara- 

 tively smooth mucosa at the tip of the fundus. The center of 

 the cross is the attachment zone for the embryonic vesicle, and 

 its right or left arm, depending on which ovary functions, forms 

 the pathway along which the vesicle travels from the Fallopian 

 tube to the point of attachment (fig. 21, pp. 561-563). 



2. The armadillos breed during October and the early part of 

 November. A large majority of the old females are pregnant 

 before October 15, but the second year females may continue to 

 breed for some time after this period. The young are born in 

 March and April, but an occasional litter may appear in Febru- 

 ary. The period of gestation is estimated at one hundred and 

 forty days (p. 564). 



3. Except in very rare instances, young females born in March 

 or April do not breed during the succeeding fall (p. 564). 



4. A 'period of quiescence 7 of the blastocyst was discovered. 

 This period lasts for at least three weeks, and is probably similar 

 to the quiescent period of the blastocyst of the deer described by 

 Bischoff (pp. 564-565). 



5. The right and left ovaries function with equal frequency 

 (p. 567). 



6. In no case has more than one ovum been found in the uterus 

 (p. 567). 



7. The youngest specimen obtained was a typical mammalian 

 blastocyst, consisting of an outer trophoblastic layer of polygonal 

 cells, and an inner cell-mass of embryonic cells (fig. 6, pp. 571- 

 572). 



8. The entoderm differentiates before implantation occurs, 

 and arises through a migration of entodermal mother-cells from 

 among the embryonic ectodermal cells of the inner cell-mass. 

 These entodermal cells, migrate, either directly or after having 

 undergone division, to the under surface of the mass, where they 



