Fig. 9 Egg-cylinder of albino 
rat, in which the antimesometrial 
and mesometrial portions of the 
proamniotic cavity have failed to 
unite to form a single or definite 
proamniotic cavity. X 200. Rat 
No. 41, 8 days, 16 hours, after the 
beginning of insemination. ect.pl., 
ectoplacental cone or “Triger; 
p.ect., parietal or transitory ecto- 
derm; v.ent., 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. 
a 
Mas yrrs\ (9) % GaN or (os 
ae ve ‘o ey 5 4 
a OD 
pe 
ip : im 
a) 
aS ee 
Om at 
RIO AO 
08 O@ S 
EOS POS 
sala, 
ae 
iA 
~ 
[Es 
—(_pr,emb, ect. 
