Fig. 26 Longitudinal sections of egg-cylinders ot 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 Triiger; 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 proamniotie cavity, developing in the ectodermal node; pr.emb.ect., 
primary embryonic ectoderm; ect.ves., ectodermal vesicle; met.pr., mesometrial 
portion of the proamniotie cavity, developing in the extramebryonic ectoderm. 
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