Laboratory Exercises 379 
(c) Note the transparent, watery appearance of the albumen 
(white of the egg). 
The albumen supplies in liquid form the food by which the 
chick grows within the shell. 
(d) Examine the shell and notice the air-space usually found 
near the large end. Observe the two tough membranes best 
seen at the air-space where the membranes separate. 
The air-space furnishes a readily available supply of fresh air 
to the embryo chick. The two membranes prevent the too rapid 
THINNER ALBUMEN. GERI SPO7, OR DISC, 
(we) OR VESICLE 
THICKER ALBUMEN. DARK YOLK 
(were) 
LIGHT YOLK 
CHALAZA CHALAZA 
CONCENTRIC LAYER OUTER MEMBRANE 
INNER MEMBRANE MIR SPACE 
Fic. 152.—Section of an egg. 
evaporation of moisture through the pores of the shell, but allow 
oxygen to enter the egg and carbon dioxid to pass out. 
(e) By placing a section of the shell under the lens, indentations 
or pores in the shell may be observed. 
These thinner parts permit the gases to pass through the shell 
more readily. If the pores of the shell are closed by oil, varnish, 
dirt, or broken egg, the chick will be smothered. 
(f) Note the pigment of the shell, which gives to each egg its 
characteristic color. 
Observe how the first eggs laid for a brood are more pronounced 
in color, and how the color pigment decreases with each egg that 
is laid, due to exhaustion of the supply. 
3. The structure of a boiled egg. — Crack the large end of a 
hard-boiled egg carefully. Remove the shell, piece by piece, to 
avoid tearing the shell membrane. 
