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’ 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 
(p567): 
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 imner cell-mass. 
These entodermal cells, migrate, either directly or after having 
undergone division, to the under surface of the mass, where they 
