334 FARM ANIMALS 
embryo, some are veins bringing the blood back again. 
The heart commences pulsating about the second or third 
day. When blood circulation begins impure air is re- 
vived by the oxygen, obtained from the air that passes 
in and out of the holes of the shells. Were you to coat 
over with wax an incubating egg, the embryo would die 
from want of fresh air. 
8. Handling incubating eggs.— Eggs during incubation 
require cautious handling; otherwise the delicate blood 
vessels, which form a perfect maze of tracery over the 
yolk, may be disturbed or injured. The less that eggs 
are moved about, the less danger of damaging the fragile 
and delicate interior. Many dead embryos in the incu- 
bator are the result of careless turning and handling. In 
testing out a hatch to remove the infertile eggs, it is very 
important that the work be done with careful movements 
in order not to shake or twist the sensitive and delicate 
organs inside the egg. 
Eccs To Avoip FoR HATCHING 
Note the ridges and imperfect shape of the shell: avoid such in 
selecting eggs for hatching. 
