Our lack of concern about coloration is due to the fact that, with the exception of the blue spots on the flanks and posterior surfaces of the thighs in some species, the coloration of _Smilisca_, consisting of a pattern of irregular dark marks on a paler dorsum and dark transverse bars on the limbs, is not much different from that of many other Neotropical hylids. Blue is a structural color, rare among Amphibia, which is achieved by the absence of lipophores above the guanophores. Thus, the incident light rays at the blue end of the spectrum are reflected by the guanophores without interference by an overlying yellow lipophore screen. According to Noble (1931), lipophores are capable of amoeboid movement that permits shifts in their positions, between or beneath the guanophores. We do not know whether this behavior of lipophores is widespread and is effected in response to environmental changes, or whether it is a genetically controlled attribute that is restricted in appearance. If the latter is the case we must assume that the prototype of _Smilisca_ possessed such an attribute which was lost in _S. baudini_, _phaeota_, and _puma_. The development of blue spots is not constant in _S. sordida_ and _S. sila_; in _S. cyanosticta_ the spots range in color from blue to pale green. The coloration of the tadpoles is not distinctive, except for the presence of dorsal blotches on the tails of _S. sila_ and _sordida_. However, the similarity in pattern cannot be interpreted as indicating close relationships because nearly identical patterns are present in _Hyla legleri_ and some species of _Prostherapis_. This disruptive coloration seems to be directly associated with the pebble-bottom, stream-inhabiting tadpoles. In the _baudini_ group, _S. phaeota_ and _cyanosticta_ are allopatric, whereas _S. baudini_ occurs sympatrically with both of those species. The call of _S. baudini_ differs notably from the calls of _S. phaeota_ and _cyanosticta_, which are more nearly alike. Although in the phylogenetic scheme proposed here _S. sila_ is considered to be more distantly related to _S. puma_ than is _S. sordida_, the calls of _S. sila_ and _puma_ more closely resemble one another than either resembles that of _S. sordida_. _Smilisca sila_ and _puma_ are allopatric, whereas _S. sordida_ is broadly sympatric with both of those species. We assume that in their respective phyletic lines the differentiation of both _S. baudini_ and _sordida_ was the result of genetic changes in geographically isolated populations. Subsequently, each species dispersed into areas inhabited by other members of their respective groups. Selection for differences in the breeding calls helped to reinforce other differences in the populations and thereby aided in maintaining specificity. Evolutionary History