Abstract THE frequency of occurrence and significance of the temporary invasion of Heterakis gallinarum larvae into the cecal mucosa as part of the larvae’s development is controversial. Riley and James (1921) reported marked inflammation of the cecal walls of infected chickens but did not describe a tissue phase. Dorman (1928) and Clapham (1933) indicated that all larvae developed in the lumen. Uribe (1922) designated the 2nd to the 5th day post-exposure as the period when all larvae were in the “bottom of the crypts of the cecal mucosa.” According to Itagaki (1930) no larvae were found in the cecal wall but some were buried in the cecal glands where they seemed to develop to maturity. Baker (1933) observed that “larvae showed a pronounced tendency to invade” but only the anterior one half of the larvae penetrated the glandular crypts of the mucosa. Tyzzer (1934) found the larvae penetrating the epithelia of…