ect pi. 



Fig. 9 Egg-cylinder of albino 

 rat, in which the antimesometria] 

 and mesometrial portions of the 

 proamniotic cavity have failed to 

 unite to form a single or definite 

 proamniotic cavity. X 200. Rat 

 No. 41, S days, 10 hours, after the 

 beginningof inseminat ion. ect.pl., 

 ectoplacental cone or Trager; 

 p.ect., parietal or transitory ecto- 

 derm; r.eitt., visceral entoderm; 

 met.pr., mesometrial portion of 

 the proamniotic cavity; ex.ect., ex- 

 traembryonic ectoderm; a.met.pr., 

 antimesometrial portion of the 

 proamniotic cavity; pr.emb.ect., 

 primary embryonic ectoderm; +, 

 region at which, in normal de- 

 velopment, by the end of the 

 eighth and beginning of the ninth 

 day, the two portions of the pro- 

 amniotic cavity would have united 

 to form a single space, the definite 

 proamniotic cavity. 







p. ect. 



met. pr. 



ex. ect 



a. met. pr. 



— -pr.emb.ect. 



pr. emb. ent 



13- 



