1. Eggs passed in the faeces of sheep or goats or obtained from the uteri or gravid females are able to hatch in from 24 to 36 hours under suitable conditions of aeration, temperature and moisture.
2. The larvae have three preparasitic stages each separated by an ecdysis. The cuticle of the second stage is retained as a protective sheath for the third or infective stage which is reached in five to eight days after hatching.
3. Morphologically and biologically the different larvae are practically identical to those of Gaigeria pachyscelis.
4. Infection of the host takes place either by penetration of the skin or via the mouth.
5. After penetrating the skin the larvae proceed to the lungs which they reach within six days; the route taken is presumably via the blood stream.
6. In the lungs the larvae remain for about five days during which period they feed, grow and pass into the fourth stage provided with a provisional buccal capsule.
7. The larvae now migrate to the intestine presumably via the trachea, mouth and oesophages. When first seen in the intestine they have already shed their sheath, but no sex differentiation is yet evident; sex differentiation sets in about four days later. Buccal lancets also appear.
8. The larvae attach themselves to the intestinal villi and feed on the liberated blood. They grow and begin to pass into the final or fifth stage in about a week after reaching the intestine.
9. Final ecdysis takes place about 10 days later.
10. Growth continues and the egg laying stage is reached in nine to ten weeks after infection.