POLYEMBRYONIC DEVELOPMENT IN TATUSIA 609 



hohle) in Mulita; but in the Texas armadillo the enlarged space 

 is clearly an artifact. One can easily observe in the sections that 

 it has been produced by lifting up the Trager epithelium from 

 the subjacent emaciated mucosa, probably through the action of 

 the fixing and hardening reagents. It has not been observed in 

 any other specimen, either older or younger, and this leads one 

 to suspect that it is likewise an artifact in the blastocyst of 

 Mulita, especially as it does not appear in the older vesicles of 

 this animal. 



In plate 9 is shown a series of five sections from a chorionic 

 vesicle presenting a further advance hi the development of the 

 secondary buds and their accompanying embryos. The speci- 

 men is one of the finest in my collection, not only because of 

 its excellent state of preservation, but also for the reason that 

 it remained turgid while undergoing fixation, and thus gives us 

 a picture in the sections which most closely resembles that of 

 the living vesicle. 



Figure 3 is an outline reconstruction of this series, and shows 

 that the buds have made considerable progress. Buds II and 

 IV are still larger than I and III, but this inequality gradually 

 grows less and less as the buds extend outward and downward 

 beneath the entoderm. 



In the section passing through plane e to / of figure 3, the 

 general relation of the various parts is well shown. The large 

 extraembryonic cavity, lined with mesoderm, is conspicuous. 

 Above this, and separated by the thin amnion, is the amniotic 

 cavity of the ectodermal vesicle (fig. 72). The section passes 

 a little to the left of the center of the left-lateral bud, which 

 appears in section as a prolongation of the left side of the ecto- 

 dermal vesicle. The outer covering of the chorionic vesicle is 

 the entoderm, the chorionic ectoderm having already disap- 

 peared. The point at which it has broken off close to the base 

 of the vesicle is clearly seen in this and the other photographs. 



The other sections illustrated in the plate present special 

 parts of the several embryos. Thus figures 70 and 74 show 

 transverse sections of Embryo III and Embryo I, respectively. 

 In each case the primitive groove is distinct. In figure 71 the 



