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1. The principal energy sources of cave ecosystems are (a) organic matter swept underground by sinking streams, and (b) the feces, eggs, and dead bodies of animals which remain in the cave for shelter but feed outside (trogloxenes). In temperate zone caves flooding and the entrance of cold air during winter and early spring disturb the relatively constant physical conditions of the cave environment. 2. Species density, dispersal potential, and other aspects of the ecology of troglobites (obligate cavernicoles) are profoundly influenced by continuity of limestone outcrops in which the caves are developed. In the Appalachian valley, where limestone is exposed in many narrow, anticlinal strike belts, species density per unit area is high, and dispersal of troglobites through subterranean channels is severely restricted by geologic structure. In the Mississippian plateaus, where thick, caverniferous limestone is widely and continuously exposed, there are fewer species per unit area; and subterranean dispersal has taken place over considerable distances. 3. High dispersal potential leads to rich species diversity and frequent sympatry. The more complex cave communities of the Mississippian plateaus permit an increase in modal size of beetles (and perhaps other troglobites) and result in greater population density and stability. 4. Ancestors of troglobites probably entered caves first as troglophiles (facultative cavernicoles), with gene flow initially continuous between epigean and hypogean populations. Extinction of epigean populations by (chiefly Pleistocene) climatic events effected geographic and genetic isolation in the caves. 5. The mechanism of eye and pigment reduction probably involves the initial reduction in genetic variability and reconstruction of the epigenotype which accompanies the speciation process. Selection for the relatively few viable gene complexes, balanced polymorphisms, and canalization systems which are possible with the limited variability available may lead indirectly toregression of adaptively neutral characters through pleiotropy and polygeny.