COMPARATIVE ZOOLOGY. 
202 
The embryo lies with its face, or ventral surface, tow¬ 
ards the yolk, the head and tail curving towards each 
Fio. 1 TO. —Hen’s Eg", more highly developed. The embryo is enveloped by the am¬ 
nion, and has the umbilical vessel, or remnant of the yolk, hanging from its un¬ 
der surface; while the allantois turns upward, and spreads ont over the internal 
surface of the shell-membrane. (Prom Dalton’s “ Physiology.”) 
other. Around the embryo on all sides the epiblast and 
upper layer of the mesohlast rise like a hood over the 
back of the embryo till they 
form a closed sac, called the 
amnion. It is filled with a 
thin liquid, which serves to 
protect the embryo. Mean¬ 
while, another important or¬ 
gan is forming on the other 
side. From the hinder por¬ 
tion of the alimentary canal 
an outgrowth is formed 
Fu,!!, Mammalian Embryo with al- which extends bey Olid the 
iantois tally formed: 1, umbilical vesi- J 
cle, containing the last of the yolk; 2, wall of tile embryo proper 
amnion; 3, allantois, on which thefringes . . O' r r . 
of the placenta are developing. (Prom into the Cavity of the amni- 
Dalton’s “ Physiology.’’) 
on and spreads out over the 
whole inner surface of the shell, so that it partly surrounds 
both embryo and inner layer of the amnion (amnion jprop- 
