Numerous investigators have attempted to find specific environmental conditions conducive to hatching of eggs of floodwater mosquitoes. From these investigations two general facts are well known, (1) that eggs of certain species usually hatch when submerged in their natural habitats during the spring or summer and (2) that at other times eggs may remain dormant through one or more periods of inundation only to hatch later. Many explanations have been advanced to explain this apparently erratic behavior. None of these adequately takes into account the fact that hatching of an egg depends not only on the presence of a proper stimulus but also on prior events leading to completed conditioning of the egg. Consequently other investigators have been unable to confirm previous data. It is not surprising, therefore, that a great variety of methods have been proposed for inducing hatching.