v.v., the vitelline veins.
al., the allantois.

Figure 2. Chick about sixth day.

Figure 3. Development of heart.

Figure 4. Development of the eye.

Figure 5. Chick about the sixteenth day.
A.M. is the amnion surrounding the embryo. Note particularly how the
allantois (al.) has spread over surface of shell and how the yolk sac is
shrivelled.

Figure 6. Figures to illustrate the relative function and importance of
allantois and yolk sac in bird and mammal. In the fowl, however, the
blood-vessels of the allantois also probably absorb the albumen of the
egg, and may excrete urea into the egg-space.

Figure 7. Simplified figure of the embryonic circulation, for comparison
with the similar figures annexed to Dog-Fish and Rabbit.

{Lines from Second Edition only.}
[A.C., anterior cardinal.
Ao., Aorta.
Br4, sixth aortis arch (fourth branchial).
C.S. Cuvierian sinus.
H., the heart.
I.C., inferior cava.
P.C., posterior cardinal vein.
Tr.A., truncus arteriosus.
v.v., vitelline vein.]

Figure 8. Chick on the nineteenth day.

{Illustration: Diagram Sheet 24.}

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