In 1936, Whorf was appointed Honorary Research Fellow in Anthropology at Yale, and he was invited by Franz Boas to serve on the committee of the Society of American Linguistics (later Linguistic Society of America). In 1937, Yale awarded him the Sterling Fellowship. He was a lecturer in Anthropology from 1937 through 1938, replacing Sapir, who was gravely ill. Whorf gave graduate level lectures on "Problems of American Indian Linguistics". In 1938 with Trager's assistance he elaborated a report on the progress of linguistic research at the department of anthropology at Yale. The report includes some of Whorf's influential contributions to linguistic theory, such as the concept of the allophone and of covert grammatical categories. has argued, that in this report Whorf's linguistic theories exist in a condensed form, and that it was mainly through this report that Whorf exerted influence on the discipline of descriptive linguistics.