Eggs of Melanoplus bivittatus (Say) possess a special water-absorbing area, the hydropyle, similar in function to that of M. differentialis (Thos.). The extent of hydration was measured as eggs of M. bivittatus developed at 25 °C. on contact moisture. The total amount of water absorbed amounts to about 60% of the original weight of the egg. Absorption is negligible for the first four days, is maximal on the eighth and ninth days, and later may exhibit a second period of minor increase and decline, which varies in time of occurrence. About 88% of the total absorption occurs during anatrepsis. Eggs denied contact moisture from the time of oviposition develop to the end of anatrepsis and remain viable for long periods, provided desiccation is not severe. When contact moisture is provided, such eggs hydrate very rapidly and continue development with a retardation of two or three days. Extra moisture from the environment is essential for the revolution and katatrepsis of the embryo.