After her first year of graduate school, Carson became a part-time student, taking an assistantship in Raymond Pearl's laboratory, where she worked with rats and "Drosophila", to earn money for tuition. After false starts with pit vipers and squirrels, she completed a dissertation project on the embryonic development of the pronephros in fish. She earned a master's degree in zoology in June 1932. She had intended to continue for a doctorate, but in 1934 Carson was forced to leave Johns Hopkins to search for a full-time teaching position to help support her family during the Great Depression. In 1935, her father died suddenly, worsening their already critical financial situation and leaving Carson to care for her aging mother. At the urging of her undergraduate biology mentor Mary Scott Skinker, she settled for a temporary position with the U.S. Bureau of Fisheries, writing radio copy for a series of weekly educational broadcasts entitled "Romance Under the Waters". The series of 52 seven-minute programs focused on aquatic life and was intended to generate public interest in fish biology and in the work of the bureau, a task the several writers before Carson had not managed. Carson also began submitting articles on marine life in the Chesapeake Bay, based on her research for the series, to local newspapers and magazines.