1 Considerable variability exists in the size of ova produced by different female Bombina orientalis Boulenger in a field population in Korea. Both the mean and variance among females changed significantly between 1986 and 1987. These data, when viewed in conjunction with laboratory studies that demonstrate that the size of ova produced is very sensitive to environmental variation, strongly suggest that mean ovum size varies between breedings of individual females and is therefore a plastic feature of this population. 2 Differences in ovum size did not affect developmental time to the hatching stage, but there were large effects associated with micro-climatic temperature variation both within and between years. In 1987 the embryos in some breeding pools hatched in 2 5 days while others, in different pools, hatched in 8 0 days. 3 Ovum size significantly influenced size at the hatching stage with larger hatchlings developing from larger eggs. In general, hatching size is negatively related to temperature, but the relationship is complex; higher temperature increased the growth rate to this stage, but simultaneously truncated development time which reduces size. Hatching size is also negatively related to temperature fluctuations as a result of truncation of development time. 4 The effects of ovum size were found to have positive effects on larval size for several weeks beyond the hatching stage when larvae are most susceptible to predation. Key-words: Development, frog, Korea, maternal effects, ovum size, plasticity, tadpole Introduction Most recent studies on the complex life cycle of amphibians have focused on the metamorphic stage (e.g., Werner, 1986; Alford & Harris, 1988; Newman, 1988ab). The quantification of environmental and genetic factors that contribute to the large amount of variation that is observed in the timing of this event and growth rates prior to it have been of major concern (e.g. Berven, 1987; Travis, Emerson & Blouin, 1987). These studies are particularly interesting because it is a well reviewed observation that pre-metamorphic larvae are susceptible to a variety of abiotic and biotic factors that can impinge on their survival and affect reproductive characteristics of resultant metamorphs (Wilbur, 1984; Semlitsch, Scott & Pechmann, 1988). Recurrent abiotic themes in the larval environment include pond ephemerality and temperature, and biotic themes include predation and competition. As a result of the perception that metamorphosis is a key event in the life cycle, earlier stages of larval development have received less attention. But, there is an increasing awareness that oophagy, cannibalism and interspecific predation are common during this period (Crump, 1983; Polis & Myers, 1985). Therefore, those sources of variation in characteristics that influence susceptibility to predation during these early stages, warrant more detailed investigations (Travis, Keen & Juilianna,