Early Stages of the Pig 



29 



The middle layer or ectoderm is distinguishable earlier, and in 

 some mammals very much earlier, than the other two are dis- 



B 



Fig. 15. Pig. 



A, 4 segment stage; B, morula stage; C, blastocyst showing vacuoles; D, 4 day 

 blastocyst; E, 7 day blastocyst; al albumen layer; ec ectoderm; en endo- 

 derm ; / oil drops ; vac vacuoles ; tr trophoblast ; im inner mass. 



