Nematode egg. Scanning electron micrograph (SEM) of an egg of the parasitic nematode worm Ascaris lumbricoides. The egg has a thick sculptured protective case. These thick-shelled eggs can survive unfavourable conditions of drought, buried in the soil. The adult worm (up to 35cm long) is an intestinal parasite of humans. Infestation can cause abdominal pain, vomiting, constipation, malnutrition and anaemia. The female worm lays large numbers of eggs in the human intestine which are excreted in the faeces and ingested by a new host via contaminated water or food. This infection is known as ascariasis. Magnification: x1300 when printed 10cm high.