The development times to hatching (D) of eggs of eleven species of copepods are closely described as functions of temperature (T) by Bělehrádek's temperature function, D = a (T - α)b using the assumption that the same value of b applies to all species. The value of a is related to egg diameter among three species of Calanus, and is unaffected by the greater opacity (presumably yolkiness) of eggs of C. hyperboreas. The value of a remains as the "real" indicator of temperature adaptation, and is closely and linearly related to estimates of environmental temperature based on mean annual temperatures within the range of each species between the pole and South America, along the east coast of the Americas.