Elachistodeis ovalis (Schneider, 1799) and Ctenophryne geayi Mocquard, 1904 are two species of anuran amphibians in the family Microhylidae, whose normally fossorial life habits make it difficult to capture them outside the breeding season, when adults concentrate in puddles formed with the onset of rainfall. This study aimed to examine the characteristics of reproductive biology, specifically variation among individuals in gonad development and patterns of diet and fat accumulation in the two species. The specimens studied were captured manually or by pitfall traps in the Volta Grande area of the Xingu River, municipalities of Vitória do Xingu and Senador José Porfírio, Pará, between October 2000 and February 2001. We dissected 102 specimens of E. ovalis and 97 of C. geayi, from which the fat bodies, stomachs and ovaries of the females were isolated. The testes of the males were only categorized by size class, and all specimens had their rostro-doacal length measurements recorded. The sex ratio observed among the individuals examined was 0.41:1 for 27 males and 66 females in E. ovalis and 0.39:1 for 22 males and 57 females in C.geayi. Immature juveniles constituted 9% of the individuals in E. ovalis and 18% in C. geayi. Among adult females, 60% had ovaries with mature eggs in C.geayi, and in E. ovalis this proportion was only 10%. The rest of the females had ovaries with eggs in different stages of development. The analyses of stomach contents and fat bodies are still in progress and preliminarily indicate a large individual variation and some similarity of diet between the two species, whose composition includes a wide variety of insects, with a predominance of ants.
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