Turtle Eggs Have Several Important Parts
Like all reptile eggs, the turtle egg, which has existed unchanged for 100 million years, is a complex means of nourishing and protecting the baby turtle within.
Turtle eggs have several important parts. In the center is the embryo, attached by an umbilical stalk to the yellow yolk sac, its primary food supply (composed of sugars, starches, fats, and proteins).
Blood vessels in the lining of the yolk sac carry the nutrients to the abdomen of the embryo. (A sea turtle's egg is 55 percent yolk, compared to 33 percent for a hen's egg.)
The amniotic sac, an envelope filled with fluid that cushions the embryo from shock and protects it from impurities, surrounds both the embryo and the yolk. As the embryo grows it gives off waste products, which would destroy it if they were not eliminated.
Typical Incubation Pepiods
Time Period Type of Turtle, or Tortoise
60 days Wood turtles, many terrapins, Australian short-necked turtles
90 days Snapping turtles, map-turtles, painted turtles
150 days Common Australian snake-necked turtle, gopher tortoises, Galapagos tortoises
250 days Flat tortoises
365 days or more African bowsprit tortoises, giant snake-necked turtles
The longest recorded incubation period was 540 days, for the egg of a leopard tortoise.
In mammals, this toxic waste is dissolved and carried away through the mother's bloodstream. In turtles, the waste is transformed into insoluble uric acid, and is stored in the allantois, a sac surrounding the embryo, yolk sac, and amniotic sac.
As the embryo grows and the yolk sac shrinks, the allantois gets larger as it fills with wastes; it is also a conveyor for incoming oxygen and outgoing carbon dioxide.
A final envelope, the chorion, surrounds the allantois, amniotic sac, yolk sac, and embryo; it is a tough, resilient membrane closely associated with the eggshell that contains egg white, or albumen (40 percent of a sea turtle egg, compared to 56 percent in a hen's egg). The chorion supplies the embryo with water and some food.