POLYEMBRYONIC DEVELOPMENT IN TATUSIA 561 
METHODS 
1. Technique 
For all of the stages described in this paper, I have found Zen- 
ker’s fluid to be the most useful fixing reagent. Kleinenberg’s 
picrosulphuric acetic acid works well on attached stages, notwith- 
standing the fact that many embryologists have regarded this 
- fluid as poor for preserving the finer structures. All of the mate- 
rial has been imbedded in paraffin, dnd the sections cut either 5 or 
7 micra thick. Most of the preparations have been stained with 
acid hematoxylin, although Heidenhain’s iron-hematoxylin has 
been used for some of the earliest stages. Whole mount prepara- 
tions of the early embryonic vesicles, which were made by the 
glycerin jelly method, were found to be very useful in the interpre- 
tation of certain changes occurring in these young stages. 
2. Method of securing early stages 
In order to understand the methods employed for securing the 
young vesicles it is necessary to give a brief account of the structure 
of the uterus. The uterus of this armadillo is of the simplex type, 
like that of the primates, and gives no evidence, in its external ap- 
pearance, of being in any way adapted to accomodate a litter of 
four. Viewed from either the dorsal or ventral sides, the uterus 
proper resembles a rather blunt spear-head, with the distal or fun- 
dus part representing the tip and the proximal or cervex part 
the shaft end of the instrument. The fallopian tubes, which lie 
in the plane of the broad ligament, enter the uterus at points lying 
approximately two-thirds the distance between the cervix and the 
tip of the fundus. 
The external appearance of the non-pregnant uterus varies 
greatly, -both in the virgin and in the old female; but in this con- 
nection we are concerned primarily with the condition of the inter- 
nal surface. In the young female, two-thirds to three-fourths 
grown, the suface of the mucosa is rather smooth, and gives only 
faint indications of a folded condition, but in the adult virgin fe- 
males of two years, and especially in the old females, the uterine 
mucosa becomes greatly folded. The folds havea general distribu- 
