Fertilized egg of Ascaris lumbricoides in an unstained wet mount of stool, 200x magnification. A larva is visible in the egg.

A fertilized egg of Ascaris lumbricoides. Two divided cells are seen interior of the egg here.   Source: http://atlas.or.kr/

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 ...

Unfertilized egg of A. lumbricoides. Note the prominent mammillations on the outer layer.  

Infertile, decorticated egg of Ascaris lumbricoides

Pollen grain in a concentrated wet mount of stool. This grain looks very similar to the fertile egg of Ascaris lumbricoides, although the spine-like structures on the outer layer should ...