Similar segregation habitatwise can be demonstrated for other members of the herpetofauna. The avoidance of interspecific competition in feeding is well illustrated by three species of snakes that probably are the primary ophidian predators on frogs. _Drymobius margaritiferus margaritiferus_ is diurnal and terrestrial; it feeds on frogs at the edges of breeding ponds by day. Also during the day _Leptophis mexicanus mexicanus_ feeds on frogs in bushes and trees. At night the activities of both of these species is replaced by those of _Leptodeira septentrionalis polysticta_, which not only feeds on the frogs in the trees and bushes, but descends to the ground and even enters the water in search of food. From the examples discussed above, the importance of the three dimensional aspect of the rainforest is apparent. The presence of a large and diverse habitat above the ground is of great significance in the rainforest, for of the non-aquatic components of the herpetofauna in the rainforests of southern El Petén, 42 per cent of the species spend at least part of their lives in the bushes and trees. Another important part of the forest is the subterranean level--the rich mulch, underground tunnels, and rotting subterranean vegetation. Of the 78 species of amphibians and reptiles in southern El Petén, seven are primarily fossorial, and half-a-dozen others are secondarily fossorial. Probably the fossorial members of the fauna are the least well represented in the collection, for such widespread species as _Dermophis mexicanus mexicanus_, _Rhadinaea decorata decorata_ and _Tantilla schistosa schistosa_ were expected, but not found. In the following discussion of the ecological distribution of amphibians and reptiles in the rainforest I have depended chiefly on my observations made in southern El Petén, but have taken into consideration observations made on the same species in other regions, together with reports from other workers. The reader should keep in mind that the evidence varies from species to species. Of some species I have observed only one animal in the field; of others, I have seen scores and sometimes hundreds of individuals. For species on which I have few observations or rather inconclusive evidence, the circumstance of inadequate data is mentioned. In analyzing the ecological distribution within the forest, it is convenient to recognize five subdivisions (habitats); each is treated below as a unit.