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 in 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 f 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 
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