Title: Phylum Aschelminthes | Introduction to Medical Parasitology
Headings: Introduction to Medical Parasitology
Phylum Aschelminthes
Class Nematoda
Generalized structure of male (A) and female (B) nematode
Introduction to Medical Parasitology

Content: The phasmids include most soil nematodes, most parasites of insects and vertebrates. The aphasmids are mainly aquatic forms and a few parasitic ones. Life cycle
Life cycles differ greatly among the many nematodes that are parasites of man. Mature female worms produce eggs, which pass out of the body with faeces. Most of the eggs are produced when they are not embryonated and become embryonated in the soil. The embryonated eggs are ingested and under the action of the gastric juices of the host, the larvae are liberated from the eggs. In some parasites, such as Ascaris, the larvae penetrate the wall of the small intestine and migrate to the lungs via the blood. From the lungs, they reach the pharynx and finally settle in the small intestine, where they will attain maturity, mate and produce eggs. In other nematodes, such as hookworms, the larvae hatch from eggs in the soil and after going through several moults become infective. These third stage infective forms enter the body through the skin.