Although there is not an abundance of data concerning the seasonal activity of the fauna, what is available shows some interesting correlations with the environments. During the dry season in the scrub forest there is essentially no amphibian activity; an occasional _Rana pipiens_ may be seen along a river, or a _Bufo marinus_ may be seen at night. In the rainforest the terrestrial-breeding amphibians are active during the dry season. _Eleutherodactylus rugulosus_ is found at night or by day along streams. _Eleutherodactylus rhodopis_, _Microbatrachylus pygmaeus_, and _Bufo valliceps_ are active during the day; these plus _Bolitoglossa occidentalis_, _Bolitoglossa platydactyla_, _Eleutherodactylus alfredi_, _Eleutherodactylus natator_, and an occasional _Hyla_ are active at night. With the onset of the heavy summer rains and the subsequent formation of breeding ponds, amphibian activity reaches a peak. This is especially noticeable in the semi-arid environments, where during the dry season there is little activity. Among the anurans in the isthmus the four species of _Eleutherodactylus_, the two species of _Syrrhophus_, and the one species of _Microbatrachylus_ are either known, or presumed, to lay eggs on the ground; these develop directly into small frogs. All of the other anurans deposit their eggs in water or attach them to objects over water (_Phyllomedusa_); these hatch into tadpoles, which later metamorphose into frogs. _Hylella sumichrasti_ is known to breed only in streams. All of the other species breed in ponds, but at times some species deposit their eggs in streams; in this last group are _Bufo valliceps_, _Bufo marmoreus_, _Phyllomedusa callidryas taylori_, and _Rana pipiens_. Although the ecological data are incomplete, they do show that ecological conditions differ greatly in the three major environments, different species of amphibians inhabit these environments, and that the fauna is ecologically diversified in each environment. _Distribution of the Fauna_ Plotting the distributions of species of amphibians known to live in the lowlands of the Isthmus of Tehuantepec results in an array of geographic patterns. These may be analyzed with respect to those species that are restricted either to the Gulf lowlands or the Pacific lowlands, or those that occur on both the Gulf and Pacific lowlands. Furthermore, the distributions may be analyzed with respect to those species whose ranges extend from Mexico across the Isthmus of Tehuantepec into Central America, those that reach the isthmus from Central America but do not extend into Mexico proper, and those that reach the isthmus from Mexico but do not extend into Central America. It should be kept in mind that the following analysis is of the lowland inhabitants only. Species inhabiting the foothills and mountains will be discussed later.