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[Ascaris lumbricoides]

Fertilized and unfertilized Ascaris lumbriocoides eggs are passed in stool of the infected host.  Fertilized eggs are are rounded and have a thick shell with an external mammillated layer that is often stained brown by bile.  In some cases, the outer layer is absent (known as decorticated eggs).  Fertile eggs range from 45 to 75 µm in length.  Unfertilized eggs are elongated and larger than fertile eggs (up to 90 µm in length).  Their shell is thinner and their mammillated layer is more variable, either with large protuberances or practically none.  Unfertile eggs contain mainly a mass of refractile granules.

A	B

A, B:  A. lumbriocoides fertilized eggs, with embryos in the early stage of development, in a wet mount.

C	D

C: A. lumbriocoides fertilized egg with embryo in the early stage of development, in a wet mount.  Image taken at 200× magnification.
D: Ascaris fertilized egg in a wet mount with embryo in a more advanced stage of development.

E

E A. lumbriocoides fertilized eggs in a wet mount, 200× magnification.  A larva is visible in the egg.