1. For species of insects that deposit their eggs on foliage, as Leptinotarsa decemlineata, Crioceris asparagi, and Anasa tristis, the rates of metabolism as measured by the CO2 output or the oxygen intake indicate, during embryonic development, a short formative period, followed by a very active extended growth. Those species that deposit their eggs in the soil, as Cotinis nitida and Popillia japonica, show that the formative period is greatly extended and the growth period similarly lengthened.