pr.emb- ' 



Fig. 26 Longitudinal sections of egg-cylinders of the albino rat, showing 

 the anlage of the antimesometrial and mesometrial portions of the proamniotic 

 cavity. X 200. A, rat No. 17, 8 days, 17 hours; B and C, rat No. 81, 7 days, 

 22 hours, after insemination. A, shows the very beginning of the development 

 of the antimesometrial portion of the proamniotic cavity developing within the 

 ectodermal node; C shows the beginning of the proamniotic cavity develop- 

 ing in the extraembryonic ectoderm; ect.pl., ectoplacental cone or Trager; p.ect., 

 parietal or transitory ectoderm; ex.ect., extraembryonic ectoderm; v.ent., vis- 

 ceral entoderm in B and C, the cells of this layer showing the anlage of the three 

 zones showing absorption of maternal hemoglobin; a.met.pr., antimesometrial 

 portion of proamniotic cavity, developing in the ectodermal node; pr.emb. ect., 

 primary embryonic ectoderm; ect.ves.. ectodermal vesicle; met.pr., mesometrial 

 portion of the proamniotic cavity, developing in the extramebryonic ectoderm. 



78 



