Appendix A. 
165 
cavity becomes recognizable, the organism is cadled a blastocyst 
(Figure 6). The outer cells of the blastocyst, especially those around 
the blastocyst cavity, assume a flattened shape. The flattened cells of 
the exterior blastocyst are the trophoblast. They become the 
embryo’s contribution to the placenta and other supporting 
structures. On one side of the blastocyst is a group of cells that 
project inside into the blastocyst cavity; this is the inner cell mass, or 
embryoblast, and its progeny form the body of the nevsr offspring. 
FORMATION OF THE BLASTOCYST 
Figure 6A-C: Three stages of the mammalial (blastocyst) of the pig, drawn from 
sections to show the formation of the inner cell mass. 
[Carlson, 4*^ Ed., Fig. 4-10, page 124.) 
Figure 6D: Early Blastocyst (see foDowing page). 
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