Fig. 27 Longitudinal sections ot egg-cylinders of the albino rat showing 

 fusion of the antimesometrial and the mesometrial portions of the proamniotic 

 cavities. X 200. A, rat No. 81, 7 days, 22 hours; B, rat No. 96, 8 days; C, rat 

 No. 94, 8 days, after insemination; ect.pl. , ectoplacental cone or Trager; p.ect., 

 parietal or transitory ectoderm; ex.ect., extraembryonic ectoderm; ect.ves., ecto- 

 dermal vesicle, with wall composed of primary embryonic ectoderm, at + junc- 

 tion with the extraembryonic ectoderm; a.met.pr., antimesometrial portion of 

 proamniotic cavity; met.pr., mesometrial portion of proamniotic cavity; pr.c., 

 proamniotic cavity; v.ent., visceral entoderm; pr.emb.ent., primary embryonic 

 cntoderm. 



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