608 J. T. PATTERSON 
next oldest blastocyst in the collection. In the entire blastocyst 
the primary buds with their accompanying embryonic rudiments 
stood out clearer than in the preceding specimen (No. 290), 
mainly because the chorionic ectoderm had already sloughed off 
from the upper side of the vesicle, thus giving a better view of 
the ectodermal vesicle. . 
The general arrangement of the secondary buds is identical in 
these two specimens (cf. fig. 2 and 28), but No. 175 is distinctly 
further developed. This becomes especially evident in a de- 
tailed study of the sections. In the section which passes 
through the place a to b, figure 29, bud IV is seen to be well 
defined, and the accompanying embryonic rudiment extends 
down into the tip of the bud, showing a well defined primitive 
groove (fig. 66). Anteriorly the groove becomes very pronounced, 
due in a large measure to the elevation of the medullary folds 
(fig. 67). 
In the central region of the ectodermal vesicle (fig. 68) the 
lateral walls have become distinctly thinner, and will soon reach 
a state in which the entire wall, exclusive of the embryonic por- 
tions, will Become but a single layer thick. When this condi- 
tion is once attained the ectodermal vesicle undergoes no further 
growth or expansion, but remains a small inconspicuous structure 
(common amniotic vesicle) to which the embryos remain con- 
nected by means of amniotic canals or tubes. These canals are 
developed through the extension of the secondary buds, which 
rapidly push outward and then downward along the under side 
of the entoderm, carrying with them the embryonic rudiments. 
At this point we are concerned with the beginning only of the 
tubes, and this can be seen not only in figure 66, but also in 
figure 69, especially in the case of Embryo II. 
It remains to say a word about the cavity lying just beneath 
the Trager epithelium in blastocyst No. 175. This cavity ex- 
tends throughout the greater part of the left side of the chori- 
onic vesicle (fig. 27, Cav.). If these figures are compared with 
text figure 1 of Fernandez (’09) it will be found that there is 
much similarity between them as regards this cavity. Fernan- 
dez designates it the Trager cavity (or Ectoplacentarplatten- 
