Development time (D) to hatching at any temperature (T) is accurately described by Belehradek''s function, D = a(T -[alpha])b, for several species and geographical populations of copepods from the north Atlantic and eastern Canadian Arctic. Assuming b to be the same for all species regularizes the results. The scale correction or "biological zero" ([alpha]) then be comes lowest in the arctic Calanus glacialis and highest in the temperature Acartia clausi and Tortanus discaudatus. Among different populations of Calanus finmarchicus and Pseudocalanus minutus, [alpha] varies only slightly, but seems positively related to local temperatures. Differences in a within species or between closely related species are related to differences in egg size and DNA content. The relationship between a and egg size resembles predictions from mass transfer theory, and supports Berill''s belief that control is super-imposed by surface/volume restrictions in CO2 exchange. Differnce in optical density of eggs are attributable to yolk concentration. The parameter a seems proportional to optical density, which supports Berrill''s belief that yolk simply "dilutes" metabolically active cytoplasm. Yolk does not appear to affect other parameters, which it might do if it affected diffusion, as implied in the possible biophysical basis of Belehradek''s function.