The life cycle of Cooperia punctata is direct, conforming closely to that of C. curticei. Eggs are in the 16-cell stage when passed in the feces, hatch in 20 hrs., and the 1st ecdysis takes place 30 hrs later. The 3d stage is reached 96 hrs. after hatching, at 28[degree] C. and the larvae measure about 800 [mu] in length. On ingestion by a susceptible calf, infective larvae complete the 2d ecdysis within 24 hours. The parasitic larvae are in the 4th stage at the end of the 4th day, in the 5th stage at the end of the 7th day, and are mature as early as the 11th day following infection.