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 6, 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 ill 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- 



