.B 



I i-. 27 Longitudinal sections ol egg-cylinders of the albino ral Bhowing 

 fusion of the antimesometrial and the mesometrial portions of the proamniotic 

 cavities. X 200. A. rat No. 81, 7 days. 22 hours; I'., rat No. 96, 8 days; C, r.-.t 

 Xo. 94, 8 days, after insemination; ecl.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; mel.pr., mesometrial portion of proamniotic cavity; pr.c, 

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

 entoderm. 



81 



