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, and 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 have a general distribu- 



