The site selected by the larvae of Heligmosomoides polygyrus.

Histological examination of the small intestine of mice infected with Heligmosomoides polygyrus indicates that the final site of the larvae is in the circular muscle layer of the muscularis externa of the anterior small intestine. The larvae become embedded in the muscle between the first and third days after infection and are subsequently sequestered by a localized leucocytic response. There is no evidence of a true cyst. Histological evidence suggests that the larvae actively feed on the tissues of the host during their development.