[Illustration: FIG. 2. Rain pond in forest at Toocog. This was a breeding site for six species of frogs.] Ecology of the Herpetofauna Our two visits to Chinajá and Toocog afforded the opportunity to gather data on the ecology of the rainforests of southern El Petén and to study the relationships between the environment and members of the herpetofauna. Tropical rainforests present the optimum conditions for life, and it is in this environment that life reaches its greatest diversity. Here, too, biological inter-relationships are most complex. This complexity is illustrated by the presence of many species of some genera, all of which are found together in the same geographic region. In the rainforests of southern El Petén there are six species of _Anolis_, five of _Hyla_, four of _Bothrops_, and three of _Coniophanes_. Obviously, the diversity of ecological niches in the rainforest is sufficient to support a variety of related species. Of the examples mentioned above, fairly adequate ecological data were obtained for most of the species of _Anolis_, which will be used to show the ecological diversity and vertical stratification of sympatric species in the rainforests. Of the six species of _Anolis_, all except _A. sericeus_ are typically found in humid forests. _Anolis sericeus sericeus_ is poorly represented in the collections from southern El Petén, where it may be in competition with _Anolis limifrons rodriguezi_ that resembles _Anolis s. sericeus_ in size, coloration, and habits. Therefore, _Anolis sericeus sericeus_ is excluded from the following discussion. The common terrestrial species is _Anolis humilis uniformis_; sometimes this small species perches or suns on the bases of small trees or buttresses of some large trees. When disturbed it takes to the ground and seeks cover in the leaf litter or beneath logs or palm fronds. _Anolis lemurinus bourgeaei_ is about twice the size of _Anolis humilis uniformis_ and is usually observed on buttresses of large trees or on the lower two meters of tree trunks. Individuals were seen foraging on the ground along with _Anolis humilis uniformis_. At no time were _Anolis lemurinus bourgeaei_ observed to ascend the trunks of large trees; they always took refuge near the bases of trees. _Anolis limifrons rodriguezi_ is found on the stems and branches of bushes. It is a small species that sometimes is observed on the ground but was never seen ascending large trees. _Anolis capito_ is about the same size as _Anolis lemurinus bourgeaei_ and lives on the trunks of large trees. In the tops of the trees lives a large green species, _Anolis biporcatus_.