A thorough autelogical investigation of Zealuctra claasseni, Zealuctra hitei, and Perlesta placida life cycles was made with emphasis on special adaptive features to the harsh, dry climate of the southwestern United States. Z. claasseni was collected from a tributary of the Red River in Cooke County, Texas, and Z. hitei was collected from the upper reaches of North Pecan Creek in Wise County, Texas, Dec., 1974-Jun., 1978. Both streams were intermittent (except a 0.3 km stretch of the Red River tributary below a spring) running only during fall-winter 1974-1975 and 1976-1977.